PDP-12 User's Manual

CHAPTER 2
CONTROLS AND INDICATORS

This chapter describes the function of the controls and indicators of the PDP-12 computer console, data termination panel, Type VR12 Oscilloscope, and the Type TU55 Tape Transport, and ASR33 Teletype.

PDP-12 CONSOLE CONTROLS AND INDICATORS

Tables 2-1 through 2-8 describe the controls and indicators located on the console of the PDP-12. Figure 2-1 provides a front panel view of the console.

DATA TERMINAL PANEL

The Data Terminal Panel refers to the area behind the door on the left side of the front of the PDP-12. Normally up to four separate panels are placed here. In addition, a storage rack to hold LINC tapes can be placed in any of the unused spaces of the Data Terminal Panel area. The four standard panels are:

1. Power Switch Panel
2. Relay and Analog Input Panel
3. Analog Extension Panel
4. Clock Input Panels

The first two are described in Tables 2-9 and 2-10 and illustrated in Figures 2-2 and 2-3; the last two are described with the associated options (AG 12 and KW12).

TYPE VR-12 OSCILLOSCOPE

Table 2-11 lists the controls and indicators of the Type VR 12 Oscilloscope. Figure 2-4 shows a front panel view of the oscilloscope.

TYPE TU55 TAPE TRANSPORT

Table 2-12 lists the functions of controls and indicators of the Tape TU55 Tape Transport. Figure 2-5 provides a front panel view of the tape transport.

MODEL ASR33 TELETYPE CONTROLS

Table 2-13 lists the functions of controls of the Model ASR 33 Teletype. Figure 2-6 provides a front view of the teletype.

Figure 2-1. PDP-12 Operator Console

TABLE 2-1. CENTRAL PROCESSOR REGISTER INDICATORS

   Indicator          Bits

Instruction Field       5
Data Field              5
Relays                  6
Instruction Register   12
Program Counter        12
Memory Address         12
Multiplier Quotient    12
Accumulator            12
Link                    1
Memory Buffer          12

Table 2-2. CENTRAL PROCESSOR MAJOR STATE INDICATORS

Indicator             State 

    F             Instruction Fetch
    D             Deferred Address
    E             Instruction Execution
    E2            Instruction Execution 2
    Int           Program Interrupt
    WC            Word Count
    CA            Current Address
    B             Break
    TB            Tape Break

TABLE 2-3. CENTRAL PROCESSOR MISCELLANEOUS INDICATORS

 
Indicator             Interpretation When Lit 

   Skip               Skip Flip-Flop is set 
   Flo                Overnow Flip-Flop is set 
  8 Mode              Processor is in PDP-8 Mode 
 Linc Mode            Processor is in Linc Mode 
   Run                Processor is running 
   Auto               Auto Restart Flip-Flop is set 
   Trap               Instruction trap is enabled 
 Int Pause            An internal pause is occurring 
    Ion               Program interrupt facility enabled 
 I/O Pause            An I/O Pause is occurring 

 
Indicator    State             When lit, indicates that: 

   I         Idle              The tape processor is in the Idle state. 
   S         Search            The tape processor is in the Search state. 
   B         Block             The tape processor is in the Block state. 
   C         Check Word        The tape processor is in the Check Word state. 
   T         Turn Around       The tape processor is in the Turn Around state. 
  IP         In Progress       A tape operation is in Progress. 

 
Indicator   Interpretation                     Function 
 
  XA     Extended Address mode   The Processor is in the Extended 
                                 Address Mode.

  NP        No Pause mode        Indicates that the processor is in the No
                                 Pause mode. 

  MK       Mark flip-flop        Indicates that the Mark flip-flop is set. 

Tape Inst     3-bit Tape         These three lights indicate the contents
              Instruction        of the 3-bit Tape Instruction register                           

I/O Preset

This switch causes the processor to halt when it is in internal Pause state during a I/O Preset tape instruction, and sets processor mode to the state of the console MODE switch. The INST Field register is set to 2 and the Data Field register is set to 3. I/O PRESET also generates the Processor I/O PRESET pulse and the I/O BUS INITIALIZE pulse thereby clearing all I/O device flags and operations.

DO

This switch causes the processor to perform one instruction. If the processor is in the LINC mode, the processor performs the instruction defined by the Left Switches (and the Right Switches if it is a double word instruction); if the processor is in the PDP-8 mode, the processor performs the instruction defined by the Left Switches.

Start 20

This switch causes the processor to start at location 20 of the currently selected Memory Bank when the processor is in the LINC mode, and at absolute location 0020 when in PDP-8 mode.

Start 400

This switch causes the processor to start at location 400 of the currently selected Memory Bank when the processor is in the LINC mode, and at absolute address 0400 when in PDP-8 mode.

Start LS

This switch causes the processor to start at the 15-bit address specified by the Left Switches and the Instruction Field Switches.

Cont

This switch causes the processor to resume operation.

Exam

This switch does the following:

1. Transfers the contents of the Left Switches into the Memory Address register.
   
2. Display in the Memory Buffer register, the contents of the absolute core address designated by the Left Switches.

Step Exam

This switch increments the contents of the Memory Address register and displays the contents of this new address in the Memory Buffer register. This incrementing extends for 10 bits in LINC mode and 12 bits in PDP-8 mode.

Fill

This switch does the following:

1. Transfers the contents of the Left Switches into the Memory Address register.
   
2. Deposits the contents of the Right Switches into the memory location whose absolute address is designated by the Left Switches and the Instruction Field Switches.

Fill Step

This switch does the following:

1. Deposits the contents of the Right Switches into the memory location whose address is in the Memory Address register.
2. Increments the contents of the Memory Address register. (This incrementing extends for 10 bits in LINC mode and 12 bits in PDP-8 mode).
3. Displays in the Memory Buffer register the contents of the location specified by the new contents of the Memory Address register.

Mode

This switch determines the mode (LINC or PDP-8) to which the processor will be set when the I/O PRESET switch is activated.

Auto

This switch is used to conditionally set the Auto Restart flip-flop. The Auto Restart flip-flop causes the processor to automatically restart at a variable time (determined by the console controls) after a processor stops for any of the following reasons:

1. Single Step Switch activated
2. F Stop address match
3. E Stop address match
4. The end of a Step Exam operation
5. The end of a Fill Step operation
6. The end of a DO switch operation

The Auto Restart Flip-flop is cleared by any of the following conditions:

1. Stop Switch pressed while processor is running
2. DO, FILL STEP, or STEP EXAM Switch activated and the Auto Switch NOT pressed.
3. A processor HALT instruction is executed (either Mode)
4. I/O Preset pulse is generated.

TABLE 2-7. TOGGLE SWITCH REGISTERS

 
Register                 Bits                     Function 
 
Left Switches             12         These switches form a 12-bit word which
                                     can be read into the accumulator with the
                                     LINC mode instruction LSW (517). This word
                                     also specifies the address to be examined
                                     when the Exam Switch is used, the address
                                     into which data will be placed when the
                                     Fill Switch is used, the stopping address
                                     for E Stop and F Stop functions, and the
                                     instruction to be performed when the DO
                                     switch is used. 
 
Right Switches            12         These switches form a 12-bit word which
                                     can be read into the accumulator with the
                                     LINC mode instruction RSW (516), or the
                                     PDP-8 mode instruction OSR (7404). This
                                     word also provides data to be stored in
                                     memory when the Fill or Fill Step Switches
                                     are used. When the DO Switch is used, the
                                     Right  Switches  contain  the  second word
                                     of two-word instructions. 
 
Inst Field                 3         These switches are a high-order extension
                                     of the Left Switches. They provide
                                     addressing information for systems
                                     equipped with 8K or more of memory, for
                                     the EXAM, FILL, Start LS, E Stop and
                                     F Stop functions. 

Sense Switches             6         These switches are individually
                                     interrogated by LINC mode skip 
                                     instructions, thereby enabling user
                                     control of program branching. 

Stop -

This switch causes the processor to stop at the end of every instruction. For the purposes of the Stop switch, Traps, Interrupt, Tape Break, and single- cycle Data Break are considered to be single- cycle instructions. During a three-cycle Data Break, the processor is stopped after the break cycle.

Single Step -

This switch causes the Run flip-flop to be cleared thereby disabling the timing circuits at the end of one cycle of operation. Thereafter, repeated operation of the Cont switch steps the program one cycle at a time so that the operator can observe the contents of registers in each major state.

Fetch Stop -

This switch causes the processor to stop when the address designated by the Left Switches matches the current address in the Memory Address register during the Fetch cycle. For systems with more than 4K of memory, the Instruction Field Switches designate the three most significant bits of the address.

Exec Stop -

This switch causes the processor to stop when the address designated by the Left Switches matches the current address in the Memory Address register during any computer cycle except a Fetch cycle. For systems having more than 4K of memory, the Inst Field Switches designate the three most significant bits of the address.

Figure 2-2. Power Switch Panel

TABLE 2-9. KNOB AND POWER SWITCH PANEL

PWR-Panel Lock

This 3-position, key-locking switch is used to turn the PDP-12 on as well as inhibit console intervention during an operating program. When fully counterclockwise, the PDP-12 power is off. When turned to the center position, the PDP-12 is turned on and the console activated. When the switch is fully clockwise, the PDP-12 is on but console control functions are totally inhibited while the PDP-12 RUN light is on. The LEFT SWITCHES, RIGHT SWITCHES, and SENSE SWITCHES remain operative.

Speaker Volume -

The volume of the speaker, which is driven by bit AC 00, is controlled by this knob. (The speaker is added to the system when the KD12 is included in the system configuration).

Auto Restart -

These two knobs control the delay period of Auto Restart after a processor stop due to E Stop, F Stop or Single instruction operation. (See Auto switch description in Table 2-6.)

Coarse and Fine -

The Coarse delay selects overlapping ranges from 10 µsec to 10 sec. The Fine control gives variation within a range of 20.1 of the selected Coarse delay.

Analog Knobs -

These 10-turn potentiometers are connected to analog input channels 0-7 of the AD12 Analog- to- Digital Converter. These knobs therefore provide eight continuously variable parameters within the range of +/- 512 for program usage.

Figure 2-3. Relay and Analog Input Panel

TABLE 2-10. INPUTS AND OUTPUTS OF ANALOG INPUT-RELAY PANEL

Analog Inputs -

+/- 1V input connections for AD12 Analog-to Digital converter channels 10₍₈₎ - 17₍₈₎.

Relay Contacts -

One form C set of contacts for each of the six system relays is available at the binding posts.

Extension Scope -

This 24-pin connector is used to connect an extension scope for remote operations, multiple displays, or photographing of display output. See the VC12 description for pin connections and drive characteristics.

Figure 2-4. Type VR12 Oscilloscope

TABLE 2-11. VR12 DISPLAY SCOPE CONTROLS

CHANNEL SELECT -

Select which of two intensity channels will cause scope display.

BRIGHTNESS -

Control level of Brightness

X GAIN -

Horizontal size of display

X POSITION -

Horizontal position of display

Y GAIN -

Vertical size of display

Y POSITION -

Vertical position of display

Figure 2-5. TU30 Tape Transport Control Panel

TABLE 2-12. TU55 TAPE TRANSPORT CONTROLS AND INDICATORS

Forward tape-motion switch (designated in Figure 2-5 by arrow pointing to the left) -

Provides forward tape motion (i.e., from right to left) only if REMOTE/OFF/LOCAL switch is set to LOCAL.

WRITE ENABLED/WRITE LOCK switch

WRITE ENABLED -

Permits TC12 control system to write information on the TU55.

WRITE LOCK -

Prevents above writing. If TC12 control system is commanded to write on tape during the WRITE LOCK setting, the control signals a write lock error.

WRITE ENABLED indicator -

Lights when WRITE ENABLE/WRITE lock switch is in the WRITE ENABLE position.

Address selector (or unit selector) -

When set to one of the numerals (designating addresses) and REMOTE/OFF/LOCAL switch is on REMOTE or OFF, the transport is selected when the line indicated by the switch wiper corresponds to the computer selection through the TC12 control. Then the transport responds to command signals from external control and can assert a write enabling signal to the control. In addition, all head channels are connected through the head relay to data bus information lines.

OFF LINE -

Prevents TCl2 control system from selecting the TU55.

REMOTE/OFF/LOCAL switch

REMOTE -

Permits TU55 to accept command and control signals from the TC12 control system; also enables head relay logic to connect all head channels to data bus information lines as soon as appropriate transport is selected.

OFF -

Inhibits operation of the G850 SCR Motor Control Modules and releases the brakes. Power for the logic components comes from power supplies associated with the external control, and therefore, the OFF position does not turn off the +10 and -15v power. The OFF position is used when loading new tape reels since it releases the motor hubs. The transport should be set to OFF when not in use.

LOCAL -

Permits forward and reverse tape-motion switch to provide tape motion in direction of arrow. Transport cannot be selected.

REMOTE indicator -

Lights only when transport is selected by the control.

Reverse tape-motion switch (designated in Figure 2-5 by arrow pointing to the right) -

Provides for motion in the reverse direction (i.e., from left to right), but only when REMOTE/OFF/LOCAL switch is on LOCAL. If both reverse and forward tape-motion switches are pressed simultaneously, the reverse motion takes place.

Figure 2-6. ASR-33 Teletype

TABLE 2-13. ASR-33 TELETYPE - FUNCTION OF CONTROLS

 
   Control                               Function 
 
REL pushbutton            Disengages the tape in the punch to allow tape
                          removal or tape loading. 
 
B. SP                     Backspaces the tape in the punch by one space,
pushbutton                allowing manual correction or rubout out of the
                          character just punched. 
 
OFF and ON pushbuttons    Control use of the tape punch with operation of the
                          Teletype keyboard/printer. 

START/STOP/FREE switch    Controls use of the tape reader with operation of
                          the Teletype. In the FREE (lowest) position the
                          reader is disengaged and can be loaded or unloaded.
                          In the STOP (center) position the reader mechanism
                          is engaged but de-energized. In the START (highest)
                          position the reader is engaged and operated under
                          program control. 

Keyboard                  Provides a means of printing on paper in use as a
                          typewriter and punching tape when the punch ON
                          pushbutton is pressed, and provides a means of
                          supplying input data to the computer when the
                          LINE/OFF/LOCAL switch is in the LINE position. 
 
LINE/OFF/LOCAL switch     Controls application of primary power in the Teletype
                          and data connection to the processor. In the LINE
                          position the Teletype is energized and connected as
                          an I/O device of the computer. In the OFF position
                          the Teletype is de-energized. In the LOCAL position
                          the Teletype is energized for off-line operation,
                          and signal connections to the processor are broken.
                          Both LINE and LOCAL use of the Teletype require
                          that the computer be energized through the POWER
                          switch.