PDP-8/e Printers

PDP-8/e Printers

Many printing options were available for the PDP8/e. This page is a summary of some of them. The original intention of this research was to provide printing capabilities to a PDP8/e running OS/8.

Every printer seems to have it's own interface. This was before printer interface was synonymous with the Centronics printer interface. Most of the interfaces are 7-bit instead of 8-bit. This doesn't present a problem because the printers tend to be ASCII with no graphics. Many didn't have lower case.

M841 Printer IOT

Code	Instruction	Description
6661	PSKF	Skip on character flag.
6662	PCLF	Clear the character flag.
6663	PSKE	Skip on error.
6664	PSTB	Load printer buffer.
6665	PSIE	Set program interrupt enable flag.
6666	PCLF PSTB	Load printer buffer and clear flag.
6667	PCIE	Clear program interrupt enable flag.

M8342, M8365 Printer IOT

Code	Instruction	Description
6660	PSSF	Set character flag.
6661	PSKF	Skip on character flag.
6662	PCLF	Clear the character flag.
6664	PSTB	Load printer buffer.
6665	PSIE	Set or clear program interrupt enable flag from AC11.
6666	PCLF PSTB	Load printer buffer and clear character flag.

PDP8/e Printers, Modules and Handlers

The following table lists the known printers, interface modules and OS/8 handlers for the PDP8/e.

Option Name	Printer	OEM	Type	Module	Interface	OS/8 Handler
LE8/E	LP01	Data Products 2310	printer	M841	Data Products	?
LP08	?	?	printer	?	?	LPSV.BN
LP8/E	?	?	printer	M8342	Centronics	LPSV.BN
LS8/E	LS01	Centronics Model 101	printer	M8342	Centronics	LPSV.BN
LC8/E	LA30 DECwriter	-	printing terminal	M8329	Centronics	LPSV.BN
LC8/P	LA180	-	printer	M8365	LA180	LPSV.BN
LV8/E	LV01	Versatec ?	printer	M8302	?	LPSV.BN
?	-	Analex 645	printer	?	?	L645.BN
LQP8/E	LQP01	Diablo 630	printer	M8366	?	LQP.BN

M8365 <=> Centronics Interconnect

The M8365 OMNIBUS printer interface has 7 unidirectional data signals and 3 control signals. The interface READY signal is connected to the printer SELECT signal. The character to print is transfered from the PDP to the printer on the 7 data signals. STROBE L is a 4μS active low pulse from the PDP to the printer that signals that a character is to be loaded from the data lines into the printer's buffer. When the printer is finished with the last character received, it responds by an active low pulse on the nACK signal. The signal nACK is connected to the interface DEMAND signal. On the rising edge of DEMAND, the printer flag is set.

So this is the data transfer/handshake sequence:

The character is place on the data signals to the printer.
The STROBE L signal is pulsed.
The printer accepts the character on the rising edge of the STROBE L pulse.
The printer transfers the character to the line buffer and/or prints the line of text.
After some delay, the printer acknowledges the transfer by pulsing the nACK printer signal.
nACK is connected to DEMAND and on the rising edge of DEMAND, the printer character flag is set.
The PDP can now sense that the printer is ready for the next character.

The follow table describes the interconnection between the M8365 parallel printer interface module and Centronics printer interface using an IBM PC cable. The interconnection is completely passive.

M8365 J1	M8365 J1	M8365 J1	CP36	CP36	IBM PP	IBM RIBBON
1	A
2	B
3	C
4	D	NC	9	DATA 8	9	17
5	E
6	F
7	H
8	J
9	K
10	L
11	M	GND	22	GND	22	18
12	N	ONLINE	13	SELECT	13	25
13	P
14	R
15	S
16	T
17	U
18	V
19	W	GND	24	GND	24	22
20	X	DEMAND	10	ACK L	10	19
21	Y
22	Z
23	AA	GND	25	GND	25	24
24	BB	P03	4	DATA 3	4	7
25	CC	GND
26	DD	P07	8	DATA 7	8	15
27	EE	GND	20	GND	20	14
28	FF	P04	5	DATA 4	5	9
29	HH	GND	21	GND	21	16
30	JJ	P01	2	DATA 1	2	3
31	KK	GND	23	GND	23	20
32	LL	P02	3	DATA 2	3	5
33	MM
34	NN
35	PP	GND
36	RR	P06	7	DATA 6	7	13
37	SS	GND	26	GND	18	10
38	TT	P05	6	DATA 5	6	11
39	UU	GND	19	GND	19	12
40	VV	STROBE	1	STROBE L	1	1
			14	AUTO FEED	14	2
			32	FAULT L	15	4
			31	INIT L	16	6
			36	NC	17	8
			11	BUSY	11	21
			12	PAPER END	12	23
			15	NC
			16	GND
			17	GND
			18	+5V
			27	GND
			28	GND
			29	GND
			30	GND
			33	GND
			34	NC
			35	NC

J1 is the 40pin BERG connector on the M8365 board. The pin is designated by ribbon cable conductor number, DEC alphabet letters and signal name.
CP36 is the Centronics printer pin number and signal name.
IBM PP is the DB25 pin number for the signal.
IBM RIBBON is the ribbon cable conductor number to an IDC cable connected to the DB25 connector.