This chapter contains descriptions of all the standard prewired I/O bus options which are available with the PDP-12. It describes the peripheral logic expander, BAI 2, and options contained within the panel, as well as the most commonly used PDP-8 and PDP-12 family of I/O bus options. In general, most PDP-8 family of options can be operated without modification on the PDP-12 1/0 bus. The reader, therefore, should refer to the DEC Small Computer Handbook ( 1970) for additional information.
Prewired options and options contained in the BAI 2 Peripheral Expander panel derive their power from the PDP-12 power supply. The Peripheral Expander contains the necessary buffering to provide the isolation and current driving requirements for 1/0 devices. The control logic for these options is contained in plug-in modules;
therefore, when one of these options is added, wiring changes or additions are not needed. Separate power supplies are normally included with all the other options.
Option Groupings Option Type Number
a. Pre wired
Teletype Model 33 ASR
Additional Teletype or Dataphone DPI 2-A,B
Real-Time Interface KW12-A
Fixed Interval Clocks KW12-B,C
LINCtape to DECtape format converter TC12-F
Digital Plotter and Control XY12
Power Fail KP12
b; Peripheral Expander Type BAI 2
4-Station TTY Control DC02-D,E
Line Printer LP12
High-speed Paper Tape Reader/Punch PC12, PP12, and PR12 Standard or Mark Sense Card Reader CR12, CM12
Data Buffers DBI 2-P, N
Option Groupings Option Type Number c. 1/0 Bus Stand Alone Peripherals
32 Station TTY Control DC02-F,G
I- and 2-Station TTY Control PT08
Line Printer LP08
Magnetic Tape Control TC58
Magnetic Tape Transport TU20
Disk Fixed Head, 3 2K DF32, DS32
Disk Fixed Head, 256K RF08, RS08
Disk Movable Head BOOK RK8, RKOl
A-D Converter AFOIA
D-A Converter AAOIA
The above groupings represent the physical organization of the PDP-12; however, the options will be described in the following order:
Option Descriptions Teletype Controls (TTY) Real-Time Interface and Clocks Disks
Tapes Line Printers Card Readers Plotters
High-Speed Paper Tape Data Buffers
Power Fail/Restart A-D Converter D-A Converter
Page Number 6-3 6-18 6-27 6-45 6-59 6-63 6-68 6-71 6-73 6-74 6-76 6-82
6.1 TELETYPE 6. 1 .1 Model 33 ASR
The Teletype Model 33 ASR is the standard Teletype device offered with the PDP-12. It may be used to type in or print out information at a rate of up to ten characters per second, or to read in or punch out perforated-paper tape at ten characters per second. Signals transferred between the Model 33 ASR and the control logic are standard, serial, 11-unit code, Teletype signals. The signals consist of marks and spaces which correspond to idle and bias current in the Teletype, and to zeros and ones in the teletype control and computer. The start mark and subsequent eight-character bits are one-unit-of-time duration, and are followed by the stop mark, which occupies two units. The 8-bit code used by the Model 33 ASR Teletype unit is the American Standard Code for Information Interchange (ASCII) modified. To convert the ASCII code to Teletype code, add 200 octal (ASCII + 2008 Teletype). Bits are numbered from right to left, from 1 through 8, with bit 1 having the least significance.
Figure 6-1 illustrates the relationship between paper tape information and the AC.
TAPE HOLE AND CHANNEL NUM-BERS
0 0 0 0
SPROCKET FEED HOLES
0 0 0 0
..._PAPER TAPE
0
0
AC BIT LOCATION-+ 4 5 6 7 8 9 10 11
NOTE:
AC BITS 0-3 ARE NOT USED.
12-0193
Figure 6-1. Relationship Between Paper Tape and Accumulator The character (number) four (4) as it would be punched on paper tape is shown in Figure 6-2.
The Model 33 ASR set generates all assigned codes except 340 through 374 and 376. Generally codes 207, 212, 215, 240 through 337, and 377 are sufficient for Teletype operation. The Model 33 ASR detects all characters, but does not interpret all of the codes that it can generate as commands. The standard number of characters printed per line is 72. The sequence for proceeding to the next line is a carriage return followed by a line feed (as opposed to a line feed followed by a carriage return). Appendix F lists the character codes for the Teletype.
6.1.2 Model 33 KSR
This Teletype model is similar to the 33 ASR, except that it does not have either a paper tape reader or punch. The control logic, however, is the same as that used with the 33 ASR.
SPROCKET FEED HOLE TAPE CHANNEL
t
BINARY CODE {t=PUNCH)
8 7 6 5 4
s
3 2OCTAL CODE 2 6
1 0 0
'---..,,---'
4
12-0193
Figure 6-2. Punched Paper Tape Format for the Number 4
6.1.3 Model 35 KSR
This unit is functionally the same as the 33 KSR. It is designed for heavy duty use and extended reliability. The control logic, however, is the same as that used in the 33 ASR.
6.1.4 Model 37 KSR
This Teletype is offered as part of the LT37-AD, AE (50 Hz) option. It has an expanded character set (i.e., upper and lower case) and control functions, and operates at 15 characters per second, both transmitting and receiving.
The LT3 7-AD option has a front panel switch which can effectively convert the unit to operate as a 33 ASR. Only upper case characters would then be received or transmitted. The LT37 option provides the following programmed operations:
a. Horizontal tab set and clear b. Motor control; on and off
c. Vertical tab; set and clear at full line increments d. Ribbon color shift
e. Reverse linefeed; full and half line increments
The LT37 is useful for the preparation of formal reports, business forms and graphical plots.
Table F-3 in Appendix F provides the character and control codes for each mode of operation.
6.1.S Teletype Controls
The basic programmed operation of the following devices is similar:
Console Teletype
Prewired Dataphone Option, Type DPl 2-A, B
Add-on Single and Dual TTY Control, Type PT08-B, C
They all transmit and receive asynchronous, full-duplex, bit-word information. These devices use control modules M706 (Receiver) and M707 (Transmitter), which are positive logic modules, or W706 (Receiver) and W707
(Transmitter), which are the negative equivalent logic control modules. These modules are fully described in the Digital Logic Handbook. The main differences in these options being controlled are:
a. Source of data (e.g., Dataphone, keyboard/display terminal, Teletype, etc.) b. Speed of operation
Slow speed devices such as Teletype are driven by the stabilized RC oscillator clock module (M452).
Higher speed requires a high stability of the selected frequency; therefore, a crystal-controlled clock module (M4QS) is used. The frequency of operation must be specified for each separate device.
c. Voltage level of inputs
Typically, DEC equipment will interface directly with EIA RS-232-B industry standard devices or the standard 0, 20 mA Teletype current loop (sometimes referred to as 0, +3V logic level). As the console Teletype is typical of the three different controls discussed in this section, it will be described in detail.
The differences which are noteworthy in the PT08 and DPl 2 will be further discussed.
6.1.5.1 PDP-12 Console Teletype Control - The Teletype control uses the standard M706 receiver, M707 transmitter, and M452 clock modules for basic logic. It will drive any one of the previously discussed Teletype models (the KSR-37 requires a slight adjustment of the clock to operate at 15 characters per second).
Serial information read or written by the Teletype unit is assembled or disassembled by the Teletype control for parallel transfer to the accumulator (AC). The control also provides the program flags that cause a program interrupt or an instruction skip depending on the availability of the Teletype and the processor.
In all programmed operation, the Teletype unit and control are considered ~s a Teletype in (TTI) for input data from the keyboard or the perforated-tape reader, and as a Teletype out (TTO) for computer output information to be printed and/or punched on tape. Therefore, two device select codes are used. Select code 03 initiates operations associated with the keyboard/reader (TTI) and select code 04 performs operations associated with the teleprinter/punch (TTO). Parallel input and output functions are performed by corresponding IOT pulses produced by the two device selectors. Pulses produced by the IOPl pulse trigger skip gates; pulses produced by the IOP2 pulse clear the control flags and/or the accumulator; and pulses produced by IOP4 initiate data transfers to and from the control.
6.1.5.2 Keyboard Reader - The keyboard and tape reader control contains an 8-bit shift register (TTI) which assembles and holds the code for the last character struck on the keyboard or read from the tape. Teletype characters from the keyboard/reader are received serially by register TTL The code of a Teletype character is loaded into the TTI so that spaces correspond to binary zeros and holes (marks) correspond to binary ones. Upon program command, the contents of the TTI are transferred in parallel to the accumulator.
When a Teletype character starts to enter the TTI, the control de-energizes a relay in the Teletype unit to release the tape feed latch. When released, the latch mechanism stops tape motion only when a complete character has been sensed, and before sensing of the next character is started. A keyboard is set when an 8-bit computer character has been assembled in the TTI from a Teletype character. The program must sense the condition of this flag with a KSF instruction, and, if the flag is set, issue a KRB instruction which clears the AC, clears the keyboard flag, transfers the contents of the TII into the AC, and enables advance of the tape feed mechanism. Program interrupt can be controlled by the LINC mode instruction ESF (0004) (refer to Paragraph 3.3.16). This instruction either enables or inhibits interrupts when either the TTI or TIO flag is set.
6.1.5.3 Instructions - Instructions for use in supplying data to the computer from the Teletype are as follows:
KSF Skip on Keyboard Flag sequential instruction is skipped.
If Keyboard Flag= 1, then PC+ I -+ PC KCC Clear Keyboard Flag
Octal code: assembled into the TTL In either case, when the character is completely assembled in the TTI, the hardware sets the keyboard flag.
0-+AC