REMEX Paper Tape Reader/Spooler Serial Adapter

I acquired a very nice Remex paper tape reader, and found some information about its interface on the Internet. It is parallel interfaced, and there is some handshaking involved in its operation. So, I built a small microcontroller-based interface to have it work much like my other paper tape readers, controllable with a handshaking line, and serial output.

It is entirely possible that this interface is "standard" for PTR's used in CNC machinery - when this was built, I have reason to believe that Remex was a market leader in this area. Therefore, this might be possible to use on other parallel-connected PTR's - such as a DECITEK that I have waiting to try out.

Note on Figure 2 that this is not a wire-wrap DB-25 shell; these are getting hard to find, so I made one.

Design and Coding

I first used a PIC 16F84, but I switched to a Scenix/Ubicom SX18 because I have an SX-KEY and it's much easier to debug with it. The SX-18 in a DIP package has been discontinued; however, a nearly identical SX-28 is a skinny 28 pin DIP is the recommended through-hole replacement. Just be glad they're still making DIP's at all.

Embarrassingly, I find myself using the SX debugger and chip as a logic analyzer. After you've done this kind of work for a while, this actually seems like a good idea. I've found with software or firmware, if you can't figure out a problem with a good debugger that you know how to use well, you should look for another line of work! I have never failed to find a software or firmware bug with proper debugging tools - be it a protocol analyzer, logic analyzer, scope, or ICE/ICD. I'd almost rather hire a mediocre programmer with good debugging and problem-solving skills than a programmer who writes elegant code that doesn't quite work.

The circuit is simple, a processor, a crystal at 10-50 Mhz and reset resistor. The MAX-232 type chip handles RS-232 output without having weird power supplies. Note: I have seen these chips, notably the TI version, oscillate very badly and get hot if you leave inputs open and untied. I would definitely steer these with pullup resistors.

The Remex DB-25 parallel interface is as follows (NOTE: your reader may differ, see below)

Pins 1-8 Data bits 0-7, inverted
Pin 9- data available, active high
Pins 11,12,13 -GND
Pin 16-Advance motor, active low. If you leave it low instead of pulsing it, the motor spins continuously.
Pin 23-5 volt source, fused on my unit at 2/10A. The fuse is removable (I discovered this after blowing it). Not
having a replacement, I soldered in a Picofuse at 1/2A. Hopefully, this is good; in either event, this amperage can definitely power this board.

I would definitely check ALL PINS for odd voltages on your unit FIRST. Manufacturers and end-users both were known to put very strange functions on a DB-25. At least this one was fused.

The RS-232 output (for a DB-25, which you OUGHT to be using on the classic computer you're hooking this up to, would have 3 for the RS-232 output, 7 for ground, and 4 for the "READ" handshaking line as input to the MAX chip (suggested - you may want to use another-see code).

The interface board is designed to be plugged into the back of the Remex.

The Scenix/Ubicom pinouts are described in the source code, here. It would not be hard to convert this to a PIC.

The asm output, suitable for input to an SX-KEY is here.

If you're interested and don't have a programmer, email me at and I can sell you a preprogrammed chip inexpensively.

I use a compiler called C2C, which is not a great compiler, but it's cheap (or a limited version is free on trial), and it can compile for Scenix/Ubicom or PIC chips, many varieties. Because it is a little quirky, it's not necessarily for the beginner although the price might make it seem so. This web site has not been updated for a while and I'm not sure that it is still available for sale.

I can now read paper and mylar tape from this reader to my PDP/8e clone.

Figure 1. Remex PTR.

Figure 2. Serial Adapter. Not much to it!