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Connect a Standard IBM Compatible Printer to your TRS-80

or Tandy 1000! Now you can connect your favorite PC Printer to your TRS-80 or Tandy 1000.

~by Brian K. Hahn ~

 

The original TRS-80's and Tandy 1000's are great little

machines.  The only real problem they had was the inability

to connect a standard off the shelf PC compatible printer to

them.  For the most part when you bought a Tandy

machine you were forced to buy a Tandy DMP 110 or 130

dot matrix printer, which because of a non-standard pin-out

configuration could not even be used on an IBM machine. 

The answer came a few years later when the Canadian

branch of Radio Shack produced cables out of their Tandy

Electronics Division from Barrie Ontario.

 

For years InterTan Corporation the international independent

arm of Radio Shack sold a printer cable that would allow a

person to connect a Tandy 1000 and TRS-80 Models I

through IV to and standard IBM compatible printer.  These

cables although available nationally in Canada are not well

known in the USA.  Today, many Radio Shack stores in

Canada have no corporate knowledge of these gems. 

Worse yet, National Parts no longer sell them.  Why is this important? 

 

Today, I have my TRS-80 Model IV connected to my LaserJet 4 Plus using Scripsit Pro.  Over the years, I have had

many people asking me to source these cables which have become all but extinct.  Even a comprehensive search of

eBay and Google failed to locate them.  This week I took my only cable apart and pulled out my trusty continuity

tester and I mapped out this printer cable so you too can modify your existing TRS-80 line printer cable  or built a new

one. 

 

There is no better thrill than seeing laser quality print come on a document you nursed on your TRS-80 or even the

Tandy 1000.  This is just one more reason to grab your Windex bottle and wipe off your old 8bit machine. 

 

I hope you find this information useful, and I would encourage someone out there to start building these cables and

selling them online.  For the full article follow the full story link. 

 

One would think that Tandy had again produced a computer that

was not compatible with the industry standard when they built the

TRS-80 and the Tandy 1000's.  In fact what they had done was

include THE accepted Centronics standards of the day.  The

culprits in this story are actually IBM Corporation and Epson

America arguably the only computer hardware companies big

enough to cause the biggest name in little computers a problem,

Tandy.

 

By the early 1980's many computer companies had included the

Centronics interface in their systems to provide line

printer capabilities.  In fact, the Tandy computers and many other

Personal Computers of the day could swap printers

at will. 

 

In August of 1981 IBM and Epson conspired to develop a new IBM standard parallel interface based on the DB25 pin

connector.  The shear financial weight of these companies pulled the entire market in their direction and today your

Windows computer's printer interface is the IBM standard.  Even the term Centronics interface had become the IBM

standard and the original specifications had almost all but disappeared.

 

Tandy Corporation, who had a very large share of the marketplace hung onto the original line printer interface for

years.  In fact the 80286 based office computers all the way up to the Tandy 3000

still had the original pin-outs, but they had changed from the edge card to the DB-

25 connector.  If you tried to connect your Epson printer into a Tandy 3000 using

a standard IBM printer cable, all that would happen is the printer would shut down. 

This became a sore point for many Tandy users and the company had to act. 

InterTan Corporation did and by the mid 1980's two models of these cables came

online. 

 

The following chart gives to a pin to pin matching of the Tandy edge card to the

IBM interface.  For the most part its simple matter of re-directing the pin-out

similar to what is done when making a null modem adaptor. 

 

Printer 36-Pin Connector as used by both Centronics and IBM (Unless stated)

TRS-80 Host 34-Pin DIP/Edge Connector

IBM-PC Host 25-Pin Connector

Signal Function

1

1

1

When goes LOW for 1.5usec and then HIGH, printer accepts byte from data lines

2

3

2

Data Bit 0 (LSB), LOW==0, HIGH==1

3

5

3

Data Bit 1, LOW==0, HIGH==1

4

7

4

Data Bit 2, LOW==0, HIGH==1

5

9

5

Data Bit 3, LOW==0, HIGH==1

6

11

6

Data Bit 4, LOW==0, HIGH==1

7

13

7

Data Bit 5, LOW==0, HIGH==1

8

15

8

Data Bit 6, LOW==0, HIGH==1

9

17

9

Data Bit 7 (MSB), LOW==0, HIGH==1

10

19

10

When LOW, printer has accepted a byte from data lines

11

21

11

When HIGH, Printer is Busy, do not send more data to printer

12

23

12

When HIGH, Printer has an Error Condition

13 (Centronics)

25

--

WHEN LOW, Printer is Busy, do not send more data to printer (Inverted copy of BUSY)

13 (IBM PC)

--

N/C

Not Used

14 (Centronics)

27

N/C

Twisted Pair Signal Ground for Fault (32)

15 (Centronics)

29

N/C

Ground

16

31

N/C

Ground

17 (Centronics)

33

N/C

Chassis Ground

17 (IBM PC)

--

N/C

Not Used

18 (Centronics)

N/C

--

When HIGH, Printer has power, See Notes

18 (IBM PC)

N/C

13

When HIGH, Printer is "selected", See Notes

19

2

N/C

Twisted Pair Signal Ground for STROBE*

20

4

N/C

Twisted Pair Signal Ground for Data 0

21

6

N/C

Twisted Pair Signal Ground for Data 1

22

8

N/C

Twisted Pair Signal Ground for Data 2

23

10

18

Twisted Pair Signal Ground for Data 3

24

12

19

Twisted Pair Signal Ground for Data 4

25

14

20

Twisted Pair Signal Ground for Data 5

26

16

21

Twisted Pair Signal Ground for Data 6

27

18

22

Twisted Pair Signal Ground for Data 7

28

20

23

Twisted Pair Signal Ground for Ack

29

22

24

Twisted Pair Signal Ground for Busy

30

24

25

Ground

31 (Centronics)

26

--

When LOW, Printer Resets

31 (IBM PC)

--

14 or N/C, See Notes

When LOW, Printer performs automatic Line Feed

32

28

15

When LOW, Printer has a Fault Condition

33 (Centronics)

--

--

N/C

33 (IBM PC)

30

16

When LOW, Printer Resets

34

32

N/C

Not Used

35

N/C

N/C

Not Used

36 (Centronics)

N/C

N/C

Not Used

36 (IBM PC)

--

17 or N/C, See Notes

Bi-Directional Control, See Notes

Printer 36-Pin Connector as used by both Centronics and IBM (Unless stated)

TRS-80 Host 34-Pin DIP/Edge Connector

IBM-PC Host 25-Pin Connector

Signal Function

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(c) 2004, 2005, Brian K. Hahn

 All Rights Reserved.