INTERFACE DESIGN AND CONTRUCTION
This section describes the interface modules of the PDP-12, available modules, interface conventions, and interface connections.
PDP-12 Interface Modules
PDP-12 interfacing is constructed of Digital FLIP CHIP modules. The Digital Logic Handbook describes more than 150 of these modules, all of their component circuits, and the associated accessories; i.e., power supplies and mounting panels. The user should study this catalog carefully before beginning the design of a special interface.
The interface modules of the PDP-12 are the M111, M906, M516, M660 and M623 modules. Interface signals to the computer use either a combination of the M111 and M906 modules or the M516 module. Interface signals from the computer will originate from a combination of M623 and M906 modules for data signals, and M660 modules for timing signals.
M111/M906 Positive Input Circuit (See Figure 5-20)
The M111 inverter module is used in conjunction with the M906 Cable Terminator module which clamps the input to prevent excursions beyond +3 volts and ground. The M906 also provides the pullup resistors to +5 volts.
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Figure 5-20. Typical M111/M906 Positive Input Circuit
M516 Positive Bus Receiver Input Circuit (See Figure 5-21)
Six four input NAND gates with overshoot and undershoot clamp on one input of
each gate. Pullup resistors to +5v are also provided.
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Figure 5-21. Typical MS16 Positive Bus Receiver Input Circuit
M623/M906 Positive Output Circuit (See Figure 5-22)
The M623 Bus Driver module contains twelve circuits with negative NAND's. Used
in conjunction with the M906 Cable Terminator module, the output is clamped to
prevent excursions beyond +3 volts and ground. Output can drive +5 milliamperes
at the high level and sink 20 milliamperes at the low level.
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Figure 5-22. Typical M623/M906 Positive Output Circuit
M660 Bus Driver Output Circuit (See Figure 5-23)
Three circuits which provide low impedance 100 ohm terminated cable driving capability using M Series levels or pulses of duration greater than 100 nanoseconds. Output can drive + 5 ma at the high level and sink 20 ma at the low level, in addition to termination current required by the G717 termination module. The M660 module is used in the PDP-12 for the following output signals:
IOP1, IOP2, IOP4, TS2, TS5
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Module Selection for interface Circuits of Peripheral Equipment
Two FLIP CHIP modules are of particular interest in the design of equipment to interface to the PDP-12. Complete details on these and other FLIP CHIP modules can be found in the Digital Logic Handbook.
M103 Device Selector (See Figure 5-24)
The M103 selects an input/output device according to the code in the
instruction word (being held in the memory buffer during the IOT cycle). M103
module includes diode protection clamps on input lines so that it may be used
directly on the PDP-12 positive bus.
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Figure 5-24. M103 Device Selector Logic Circuit
M101 Bus Data Interface (See Figure 5-25)
Fifteen two-input NAND gates with one input of each gate tied to a common
line. For use in strobing data off of the PDP12 I/O bus. M101 module includes
diode protection clamps on input lines so that it may be used directly on the
PDP-12 positive bus.
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Figure 5-25. M101 Bus Data Interface Logic Circuit
M Series Flip Chip Modules
The following is a list of M Series modules available from Digital Equipment Corporation that can be used in designing special interfaces and special devices. The majority of these modules are described in the Digital Logic Handbook. For those that cannot be found in the Handbook, contact the nearest Digital representative.
M Series Module Summary
Type Description M002 15 Loads Fifteen +3 volt sources each capable of driving ten unit loads. Can be used for typing off unused inputs. M040 Solenoid Driver Output ratings of -70 volts and 0.6 amp allow these two drivers to be used with a variety of medium current loads. M050 Indicator Driver Output ratings of -20 volts and 50 ma. Allow any of the twelve circuits on this module to drive a variety of incandescent lamps. These drivers can also be used as slow speed open collector PNP level shifters to -3 volt systems. M101 Bus Data Interface Fifteen two-input NAND gates with one input of each gate tied to a common line. For use in strobing data off of the PDP-8/I or PDP-12 I/O bus. Pin compatible with M111. M103 Device Selector Similar to W103 only for use with PDP-8/I and PDP-12 options. Output pulses are not regenerated but only buffered. Mill Inverters Sixteen inverter circuits with a fan-in of one unit load and Fan-out of ten unit loads. M112 NOR Gates Ten positive NOR gates with a fan-in of one unit load and fan-out of ten unit loads. M113 NAND Gates Ten two input positive NAND gates with a fan-in of one unit load and fan-out of ten unit loads. M115 NAND Gates Eight three-input positive NAND gates with a fan-in of one unit load and a fan-out of ten unit loads. M117 NAND Gates Six four-input positive NAND gates with a fan-in of one unit load and a fan-out of ten unit loads. M119 NAND Gates Three eight-input positive NAND gates with a fan-in of one unit load and a fan-out of ten unit loads. M121 AND/NOR Gates Six gates which perform the positive logic function AB + CD. Fan-in on each input is one unit load and gate fan-out is ten unit loads. M141 NAND/OR Gates Twelve two input positive NAND gates which can be used in a wired OR manner. Gates are grouped in a 4-4-3-1 configuration with a fan-in of one unit load and a fan-out which depends on the number of gates ORed together. M160 AND/NOR GATES Three general purpose multi-input gates which can be used for system input selection. Fan-in is one unit load and fan-out is ten unit loads. M161 Binary to Octal/ A binary to eight line or BCD to ten line Decimal Decoder decoder. Gating is provided so that up to six binary bits can be decoded using only M161's. Accepts a variety of BCD codes. M162 Parity Circuit Two circuits each of which can be used to generate even or odd parity signals for four bits of binary input. M169 Gating Module Four circuits which can be used for input selection. Each circuit is of an AND/OR configuration with four two input AND gates. M202 Triple J-K Three J-K flip-flops with multiple input Flop-Flop AND gates on J and K. Versatile units for many control or counter purposes. All direct set and clear inputs are available at module pins. M203 Set-Reset-Flip-Flop Eight single-input set-reset flip-flops for use as buffer storage. Each circuit has a fan-in one unit load and a fan-out of ten unit loads. M204 General Purpose Four J-K flip-flops which can be Buffer and Counter interconnected as a ripple or synchronous counter or used as general control elements. M206 General Purpose Six D type flip-flops which can be used in Flip-Flops shift registers counters, buffer registers and general purpose control functions. M207 General Purpose Six single input J and K type flip-flops Flip-Flops for use in shift-registers, ripple counters, and general purpose control functions. M208 8-Bit Buffer An internally connected 8-bit buffer or shift register. Provisions are made for gated single-ended parallel load, bipolar parallel output, and serial input. M211 Binary Up/Down A six bit binary up/down ripple counter Counter with control gates for direction changes via a single control line. M212 Left-Right Shift An internally connected left-right shift Register register. Provisions are made for gated single-ended parallel load, bipolar parallel output, and serial input. M213 BCD Up/Down One decade of 8421 up or down counting is Counter possible with this module. Provisions are made for parallel loading, bipolar output and carry features. M230 Binary to BCD Shift One decade of a modified shift register Register Converter which allows high speed conversion (100 nsec per binary bit) of binary data to 8421 BCD code. System use of this module requires additional modules. M302 Dual Delay Two pulse or level triggered one-shot delays Multivibrator with output delay adjustable from 50 nsec to 7.5 msec. Fan-in is 2.5 unit loads and fan-out is 25 unit loads. M310 Delay Line Fixed tapped delay line with delay adjustable in 50 nsec increments from 50 nsec to 500 nsec. Two digital output amplifiers and one driver are included. M360 Variable Delay Continuously variable delay line with a range of 50 nsec to 500 nsec. Module includes delay line drivers and digital output amplifiers. M401 Variable Clock A gateable RC clock with both positive and negative pulse outputs. The output frequency is adjustable from 10mHz to below 100 Hz. M405 Crystal Clock Stable system clock frequencies from 8KHz to 10MHz are available with this module. Frequency drift at either the positive or negative pulse output is less than .01% of the specified frequency. M410 Resonant Reed A stable low frequency reed control clock similar to the M452. Stability in the range 0°C to 70°C is better than 0.15%. For use with communications systems and available with only standard teletype and data set frequencies. M452 Teletype Clock Provides 880Hz, 440Hz, and 220Hz square waves necessary for clocking and M706 and M707 in a 110 band teletype system. M501 Schmitt Trigger Provides a regenerative characteristics necessary for switch filtering, pulse shaping, and contact closure sensing. This circuit can be AND/OR expanded. M502 Negative Input Pulses as short as 35 nsec can be level Converter shifted from -3volt systems to standard M- Series levels by the two circuits in this converter. This module can also drive low impedance terminated cables. M506 Negative Input This converter will level shift pulses as Converter short as 100 nsec from -3volt systems to M- Series levels. Each of the six circuits on this module provide a low impedance output for driving unterminated long lines. M507 Bus Converter Six inverting level shifters which accept -3 and GRD, as inputs and have an open collector NPN transistor at the output. Output rise is delayed by 100 nsec for pulse spreading. M516 Positive Bus Six four input NAND gates with overshoot Receiver and undershoot clamps on one input of each gate. In addition, one input of each gate is tied to +3 volts with the lead brought out to a connector pin. M602 Pulse Amplifier The Two pulse amplifiers in this module provide standard 50 nsec or 110 nsec pulses for M Series systems. M617 Four Input Power Six four-input positive NAND gates with a NAND Gate fan-in of one unit load are a fan-out of 30 unit loads. M623 Bus Driver Twelve circuits organized in a manner similar to two R123 gates. Input gates are negative NAND's and the open collector NPN outputs can drive 100 ma at ground. M627 NAND Power Amplifier Six four-input high speed positive NAND gates with a fan-in of 2.5 unit loads and a fan-out of 40 unit loads. M650 Negative Output The three non-inverting level shifters on Converter this module can be used to interface the positive levels or pusles (duration greater than 100 nsec) of K and M Series to -3 volt logic systems. M652 Negative Output These two circuits provide high-speed non- Converter inverting level shifting for pulses as short as 35 nsec or levels from M Series to -3 volt systems. The output can drive low impedance terminated cables. M660 Bus Driver Three circuits which provide low impedance 100 ohm terminated cable driving capability using M Series levels or pulses of duration greater than 100 nsec. Output drive capability is 50 ma at +3 volts or ground. M661 Positive Level Three circuits which provide low impedance Driver unterminated cable driving. Characteristics are similar to M660 with the exception that +3 volts drive is 5 ma. M730 8/I Bus Positive General Purpose positive bus output module Output Interfacer for use in interfacing many positive level (0 to +20 volt) systems to the PDP-8/I or PDP-12. Module includes device selector, 12 bit parallel output buffer and adjustable timing pulses. M731 8/I Bus Negative Identical to M730 except outputs are level Output Interfacer shifted for 0 to .20 volt) systems to the PDP-8/I or PDP-12. Module includes device selector, 12 bit parallel input buffer, and adjustable timing pulses. M733 8/I Bus Negative Identical to M732 except inputs are level shifted from negative voltage systems. M901 Flexprint Cable Double-sided 36 pin flexprint cable connector. All pins are available for signals or grounds. Pins A2, B2, U1,and V1 have 10 ohm resistors in series. M902 Resistor Termintor Double-sided 36 pin terminator module with 100 ohm terminations on signal leads. Alternate ground are provided as in the M903 and M904. M903 Connector Double-sided 36 pin flexprint cable connector with alternate grounds for I/O bus cables. M906 Cable Terminator 18 load resistors clamped to prevent excursions beyond +3 volts and ground. It may be used in conjunction with the M623 to provide cable driving ability.
Construction of Interfaces
This section will provide the interface designer with additional information on design procedures, module layout, wiring, and cable selection. Additional help may be obtained from local DEC sales offices.
The PDP-12 was designed to provide the user maximum ease and flexibility in implementing special interfaces. External devices and interfaces are constructed and mounted outside of the basic machine, thereby eliminating the necessity for modifications to the basic processor. All signals to and from the computer are carried on coaxial or flexprint cables.
To implement several devices, the cables parallel connect each peripheral in a serial type form (see Figure 5-26). Three dual cables are used for program interrupt cable connections in (or out). Two additional dual cables are used for a total of five, when Data Break devices are implemented.
In general, module layout is done based on the functional elements within a system and is primarily a matter of common sense.
Digital has, however, layout conventions for I/O cabling to extend devices. The interface designer may wish to use these conventions as a guide. The general rule is DO NOT DEAD END THE I/O BUS. This means that parallel connections should always be made at each device to handle possible future expansion.
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Figure 5-26. I/O Bus Configuration
Figure 5-27 shows the I/O cable connections in an option mounting panel. Module slot locations 1 through 3 (looking at the wiring pin side) in an option mounting panel are reserved for program transfer cable connections in (or out). Module slot locations 4 to 5 are reserved for Data Break cable connections in (or out). Slot 6 is used for Sense lines.
Module slot locations 1 through 6 in the bottom half of the option mounting panel are wired in parallel with the top module slot locations 1 through 6. To continue the I/O cabling to the next device, the bottom slots are used and the I/O cable connections are exactly the same as mentioned above.
Two types of cables are recommended for I/O interface connections.
One is 9 conductor coax cable. This cable protects systems from radiated noise and cross talk between individual lines. Coax cable used and sold by Digital has the following nominal specs:
Zo = 0.005 ohm/foot nominal C = 95 +/-5 L = 13.75 pf/foot approx. (unterminated) K = 124 Nhy/foot approx. Y = 79% of velocity of light, approx (1.5 nsec/ft.)The other cable is 19 conductor (9 signals and 10 grounds), #30 gauge flat copper flexprint cable.
The total length of I/O cabling, from the PDP-12 to the last device, can be a maximum of 50 feet. This can be 50 feet of coax or a combination of coax and flexprint, in which case the flexprint cannot exceed a total of 15 feet.
Connector Selection - Of the many connectors available in the module
product line, several have particular application to I/O connectors. Price
and ordering information is available on these and other connectors in the
Digital Logic Handbook. O fparticular interest are the M903 and M904
connectors described in the subsequent paragraphs.
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Figure 5-27. I/O Cable Connections
Wiring Hints - These suggestions may help reduce mounting panel wiring time. They are not intended to replace any special wiring instructions given on individual module data sheets or in application notes. For fastest and neatest wiring, the following order is recommended.
Adequate grounding is essential. In addition to the connections between mounting panels mentioned above, there must be continuity of grounds between cabinets and between the logic assembly and any equipment with which the logic communicates.
When wire wrapping is done on a mounting panel containing modules, the wire wrap tool should be grounded except when all modules are removed from the mounting panel. This procedure should be followed, because even with completely isolated tools, such as those operated by batteries or compressed air, a static charge can often build up and burn out semiconductors.
Cooling - The low power consumption of M Series modules results in a total of about 15 watts dissipation in a typical H911 mounting panel with 64 modules. Convection cooling is sufficient for a few mounting panels, but forced air cooling should be used when a very large system is built.
IOT OPTION 00 Interrupt 01 High Speed Reader Type PR12 02 High Speed Punch Type PP12 03 Teletype Keyboard/Reader 04 Teletype Teleprinter/Punch 05 Displays. Types VC8/1 and KV8/I 06 Displays, Types VC8/1 and KV86I 07 Displays, Types VC8/1, and Light Pen Type 370 10 Power Fail Option KP8/L 11 Teletype System Type PT08 12 Teletype System Type PT08 13 Real Time Clock Type KW12 14 15 16 17 20 Memory Extension Control Option Type MC12 21 Memory Extension Control Option Type MC12 22 Memory Extension Control Option Type MC12 23 Memory Extension Control Option Type MC12 24 Memory Extension Control Option Type MC12 25 Memory Extension Control Option Type MC12 26 Memory Extension Control Option Type MC12 27 Memory Extension Control Option Type MC12 30 User Interfaces 31 User Interfaces 32 User interfaces 33 User Interfaces 34 User Interfaces 35 User Interfaces 36 User Interfaces 37 User Interfaces 40 Teletype System Type PT08 41 Teletype System Type PT08 42 Teletype System Type PT08 43 Teletype System Type PT08 44 Teletype System Type PT08 45 Teletype System Type PT08 46 Teletype System Type PT08 47 Teletype System Type PT08 50 Incremental Plotter Type XY12 51 Incremental Plotter Type XY12 52 Incremental Plotter Type XY12 53 General Purpose A/D Converters and Multiplexers, Types AF01A, AM02A, AM03A and AF04A Scanning Digital Voltmeter 54 General Purpose A/D Converters and Multiplexers, Types AF01A, AM02A, AM03A and AF04A Scanning Digital Voltmeter 55 D/A Converter Type AA01A 56 D/A Converter Type AA01A 57 D/A Converter Type AA01A, Sample and Hold Control Type AC01A and AF04A Scanning Digital Voltmeter 60 Random Access Disk File and Control Type DF32 and Synchronous Modem Interface Type DP01A 61 Random Access Disk File and Control Type DF32 and Synchronous Modem Interface Type DP01A 62 Random Access Disk File and Control Type DF32 and Synchronous Modem Interface Type DP01A 63 Card Reader Type CR12 64 Synchronous Modem Interface Type DP01A 65 Synchronous Modem Interface Type DP01A 66 Synchronous Modem Interface Type DP01A 67 Card Reader Type CR12 and Synchronous Modem Interface Type DP01A 70 Automatic Mag Tape Type TC58 71 Automatic Mag Tape Type TC58 72 Automatic Mag Tape Type TC58 73 Automatic Mag Tape Type TC58 74 Automatic Mag Tape Type TC58 75 76 DECtape Control TC01 77 DECtape Control TC01Interface Connections
All interface connections to the PDP-12 are made at assigned module receptacle connectors in the Processor Mounting Frame. Capital letters designate vertical rows of modules within a mounting frame. The letters increase frorn right to left when viewed from the wiring side. Module receptacles are numbered from top to bottom within a row. Terminals are assigned capital letters from right to left with the letters G, I, 0, and Q omitted. Double sided connectors or modules are used with the suffix number 1 used to designate tire top side of a module and the suffix number 2 used to designate the bottom side.
The module receptacles and assigned use for interface signal connections
Receptacle Function N13 SENSE LINES N14 AC, IOP, TIMING OUTPUTS N15 MB OUTPUTS N16 AC, SKIP, INT. REQUEST INPUTS N17 DATA BREAK ADDRESS INPUTS N18 DATA BREAK DATA INPUTSTerminals A1, C1, F1, K1, N1, R1, T1, C2, F2, 12, L2, N2, R2, and U2 of these receptacles are grounded within the computer and terminals B1, D1, E1, H1, J1, L1, M1, P1, S1, D2, E2, H2, K2, M2, P2, S2, T2, and V2 carry signals. Terminal A2 is +5 VDC and Terminal B2 is -15 VDC. These terminals mate with either M903 or M904 Cable Connectors.
Interface connection to the PDP-12 can be established for all peripheral equipment by making series cable connections between devices. In this manner only one set of cables is connected to the computer and two sets are connected to each device: one receiving the computer connection from the computer itself or the previous device, and one passing the connection to the next device. Where physical location of equipment does not make series bus connections feasible, or when cable length becomes excessive, additional interface connectors can be provided near the computer. All logic signals passing between the PDP-12 and input/output equipment are positive voltage levels, allowing direct TTL logic interface with appropriate diode clamp protection.
Positive level for a low logic state is 0 to 0.4 volts. Positive level for a high logic state is +2.4 to +3.6 volts.
The following table presents cable connections to the PDP-12 I/O Bus. A signal is true when its polarity matches the suffix character of its name (i.e., I00 BAC 00 (1) H will be high when AC 00 (1) and a program interrupt will be requested when the line EXT INT RQST BUS L is pulled low.)
SIGNAL I CONNECTION I SIGNAL I CONNECTION IOB XL 00 H N13B1 IOB XL 09 H N13D2 IOB XL 01 H N13D1 IOB XL 10 H N13E2 IOB XL 02 H N13E1 IOB XL 11 H N13H2 IOB XL 03 H N13H1 NOT USED N13K2 IOB XL 04 H N13J1 NOT USED N13M2 IOB XL 05 H N13L1 NOT USED N13P2 IOB XL 06 H N13M1 NOT USED N13S2 IOB XL 07 H N13P1 NOT USED N13T2 IOB XL 08 H N13S1 NOT USED N13V2 IOO BAC 00(1)H N14B1 IOO BAC 09(1)H N14D2 IOO BAC 01(2)H N14D1 IOO BAC 10(1)H N14E2 IOO BAC 02(1)H N14E1 IOO BAC 11(1)H N14H2 IOO BAC 03(1)H N14H1 IOO BIOP 1 H N14K2 IOO BAC 04(1)H N14J1 IOO BIOP 2 H N14M2 IOO BAC 05(1)H N14L1 IOO BIOP 4 H N14P2 IOO BAC 06(1)H N14M1 IOO BTS 5(1)H N14S2 IOO BAC 07(1)H N14P1 IOO BTS 2(1)H N14T2 IOO BAC 08(1)H N14S1 IOO BA INITIALIZE H N14V2 IOO BMB 00(1)H N15B1 IOO BMB 06(0)H N15D2 IOO BMB 01(1)H N]5D1 IOO BMB 06(1)H N15E2 IOO BMB 02(1)H N15E1 IOO BMB 07(0)H N15H2 IOO BMB 03(0)H N15H1 IOO BMB 07(1)H N15K2 IOO BMB 03(1)H N15J1 IOO BMB 08(0)H N15M2 IOO BMB 04(0)H N1SL1 IOO BMB 08(1)H N15P2 IOO BMB 04(1)H N1SM1 IOO BMB 09(1)H N15S2 IOO BMB 05(0)H N15P1 IOO BMB 10(1)H N]5T2 IOO BMB 05(1)H N15S1 IOO BMB 11(1)H N15V2 EXT IO BUS 00 L N16B1 EXT 10 BUS 09 L N16D2 EXT 10 BUS OI L N16D1 EXT 10 BUS 10 L N16E2 EXT IO BUS 02 L N16EI EXT 10 BUS 11 L N16H2 EXT 10 BUS 03 L N16H1 EXT SKIP BUS L N16K2 EXT 10 BUS 04 L N16J1 EXT INT RQST BUS N16M2 EXT 10 BUS 05 L N16L1 EXT AC CLEAR BUS N16P2 EXT 10 BUS 06 L N16M1 IOO B RUN (0)H N16S2 EXT 10 BUS 07 L N16PI NOT USED N16T2 EXT 10 BUS 08 L N16S1 NOT USED N16V2 EXT DATA ADD 00 L N17B1 EXT DATA ADD 09 L N17D2 EXT DATA ADD 01 L N17D1 EXT DATA ADD 10 L N17E2 EXT DATA ADD 02 L N17E1 EXT DATA ADD 11 L N17H2 EXT DATA ADD 03 L N17H1 EXT BREAK RQST L N17K2 EXT DATA ADD 04 L N1751 EXT DATA IN H N17M2 EXT DATA ADD 05 L N17L1 IOO BREAK (O)H N17P2 EXT DATA ADD 06 L N17M1 IOO ADD ACCEPTED (0)H N17S2 EXT DATA ADD 07 L N17P1 EXT INCREMENT MB L N17T2 EXT DATA ADD 08 L N17S1 IOO BB INITIALIZE H N17V2 EXT DATA 00 L N18BI EXT DATA 09 L N18D2 EXT DATA 01 L N18D1 EXT DATA 10 L N18E2 EXT DATA 02 L N18E1 EXT DATA ]1 L N18H2 EXT DATA 03 L N18H1 EXT 3 CYCLE L N18K2 EXT DATA 04 L N18J1 IOB CA INCREMENT H N18M2 EXT DATA 05 L N18L1 IOO WC N18P2 EXT DATA 06 L N18M1 OVERFLOW (0)H N18S2 EXT DATA 07 L N18P1 EXT DATA ADD 02 L N18T2 EXT DATA 08 L N18S1 EXT DATA ADD 01 L N18V2