PDP-12 User's Manual



The Data Terminal provides analog inputs and relay-controlled outputs for use by LINC mode programs. The facility includes the following:


The AD12 Analog-Digital Converter and Multiplexer consists of sixteen input channels, a multiplexer, and a 10-bit A-D converter. Eight of the channels are external inputs via phone jacks. These feed through preamplifiers to the converter. The acceptable voltage range of these inputs is +/- 1v.

The other eight channels are controlled by continuously- variable knobs mounted on the Data Terminal Panel. The knobs give ten turns lock- to- lock, providing the full 10-bit range of the converter (-777, to +777,). The knobs can be used to control speeds (as in the continuous display of data from tape), set threshold levels or other test parameters, etc.

A single LINC mode instruction selects the input channel, initiates the conversion, and transfers the contents of the buffer into the AC.

SAM - Sample

Form: SAM N
Octal code: 0100 + N, 0 <= N <= 17(8) (Basic System); 0 <= N <= 37(8) (Extended System)
Execution time: 18.2 µsec (Normal mode); 1.6 µsec (Fast sample mode)
Operation: Input channel N is selected. In normal mode, the voltage level present at the input is sampled and converted to a 10-bit number (including sign), which is assembled in the converter buffer. When the conversion is complete, the contents of the buffer are transferred to AC bits 3-11. The sign is placed in bits 0, 1, and 2.

When the FAST SAMPLE Special Function is selected [ESF with C(AC[5])=1], the order of events is reversed. The current contents of the converter buffer are transferred to the AC. Then, the specified channel is selected and a new conversion is initiated. The results of this new conversion can be read by a subsequent SAM instruction.

If a conversion is still in progress when the next SAM is encountered, the processor waits until the conversion is complete before executing the new SAM.


Six DPDT relays mounted on the Data Terminal Panel can be switched by LINC mode instructions, allowing the user to control the operation of various pieces of external equipment that are not interfaced directly with the PDP-12. The states of the relays can be examined at any time.

ATR - AC to Relays

Octal code: 0014
Execution time: 1.6 µsec
Operation: The contents of AC bits 6-11 are transferred to the Relay Buffer; the state of each relay is determined as follows:

RTA - Relavs to AC

Octal code: 0015
Execution time: 1.6 µsec
Operation: The contents of the Relay Buffer are transferred to bits 6-11 of the AC. If the relay is off, the corresponding bit will be 0; if on, the bit will be 1. Bits 0-5 of the AC are not changed.

             NC     NO
 Relay          COM         AC bit
 -----    +--><--+->  <-+   ------
          |      |      |
   0      O      O      O      6
   1      O      O      O      7
   2      O      O      O      8
   3      O      O      O      9
   4      O      O      O     10
   5      O      O      O     11

Figure 3-15. Relay Terminals and Corresponding AC Bits