| ★ HARDWARE ★ IMPRIMANTE DIVERS - KDS - 8 BIT PRINTER PORT INTERFACE ★ |
KDS 8 bit printer port interface (Amstrad Computer User) | A little bit extra (Computing with the Amstrad) |
IAN SHARPE tests the KDS 8-bit printer port ONE problem often encountered when hooking a printer up to your micro is the Amstrad's dreaded 7-bit printer port. As you may know, when you tell the printer to print, for example the letter A, a code is sent down the cable, in this case 65. All the characters you would use in normal text, including special control codes, fall in the range 0-127. In binary arithmetic 127 is 1111111 - seven 1s. The CPC's printer port is constructed to send codes up to a maximum of seven binary digits meaning that, like it or not, 127 is the maximum value you can send. This would be fine but for the fact that nearly all modern printers have character sets extending up to 255 which is 11111111 in binary - eight 1s. These extra characters won't correspond with the ones in the Amstrad's internal set but that doesn't stop them being useful for enhancing your text output - have a look in your printer manual for further details. Another problem brought about by the 7-bit port is that although many printers allow you to redefine the characters, you need the full eight bits to do it. Amstrad claims that its printer interface is built to the industry standard. but if that's the case, the printer manufacturers aren't building their machines to the same standard and it's a pity Amstrad didn't run with the crowd. Other manufacturers do and Amstrad itself did in later machines such as the PC compatibles and the DMP series of printers. Fortunately there's an answer to the problem - the 8-bit printer port from KDS. The version reviewed here is the latest model which, unlike earlier versions, is compatible with CP/M. The port consists of a small circuit board fitted with a plug and through connector. All you have to do is push it on to the printer outlet, plug your printer lead into the board and you're almost ready to run. There's a key in the plug so you can't get it the wrong way up, and once installed it's unobtrusive. To access the full eight bits from Amsdos you need to run a six-line Basic program typed in from the instructions. You save this for whenever you need it and unlike the earlier 8-bit ports, if you don't run the program the Amstrad works in 7-bit mode as though the interface wasn't there. To use the port under CP/M Plus you have to reconfigure your system disc -a copy I hasten to add. Under no circumstances should you attempt to alter the original disc supplied with the machine. The modification is fairly straightforward and involves SID, one of the utilities on your system disc. Under CP/M 2.2 you also have to reconfigure, but this time it's done by typing in another Basic listing which will modify a CP/M 2.2 disc placed in the drive. After you've done that, the port works as it should and there isn't much more to say. I've had it plugged into the back of my CPC for the last month without any problems, with or without the software. To round off, unusually for a review. I'm including a monotone screen dump. It takes advantage of the 8-bit port to give a faster, full-width dump under Amsdos and works in any screen mode. I don't know if it'll work with the old port, but it isn't a long program so there's nothing lost by having a go. Just run KDS's initialisation program followed by this one. The command installed by it is |KDUMP. As written it runs with printers like my Shinwa which use ESC K to start normal 640 dot bit image printing. If your printer uses ESC *, the dump will amend itself if you alter the CALL &9000 in line 150 to CALL 9000,1. Of course, this program won't work without the 8-bit port or its software. CWTA |
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