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COMPUTERS Adding An Extra Parallel Port Recently, we added a second parallel port to one of our old PCs and while we were at it, we upgraded the serial ports with faster UARTs as well. What we did can be applied to other machines. By GREG SWAIN I N ITS DAY, our old 25MHz 386 computer was a very impres­sive machine. Purchased new just six short years ago, it came with a 120Mb SCSI hard disc drive, a fancy Radius graphics card and a whole 4Mb of RAM. Of course, those specifications would be sneered at today but at the time, it really was the latest and the greatest. After a couple of years use in a desktop publishing role, the 386 was relegated to more mundane tasks, such as wordprocess­ing, running payroll software and These are the two cards that we added to our 486. The X-2233 serial card from Dick Smith Electronics (above) gave us upgraded serial ports, while the old printer card at right gave us a second parallel port so that we could permanently connect two printers. 82  Silicon Chip maintaining a subscriptions database. And, earlier in the year, we added an external fax/modem so that faxes could be sent directly from the computer. When it recently conked out, it didn’t take long to discov­er why. A distinctive burn mark in the middle of one of the main chips on the multi-I/O board told the tale and, as we subsequent­ly discovered, the mother­ board had failed as well. Strangely, everything else in the machine proved to be OK, including the RAM, the disc drives, the Radius video card and the power supply. As a result, the old 386’s role was taken over by a 50MHz 486 machine that had been sitting unloved in a corner of the office, itself the victim of a recent upgrading. This replacement machine came with a 250Mb hard disc drive, 8Mb of RAM and Windows 3.11. We swapped its graphics card for the Radius card from the defunct 386 (so that we could still use the Radius monitor) and we were up and running. After that, it was simply a matter of reinstalling the necessary software and copying our backup data files onto the replacement hard disc. Parallel ports Having come this far, we decided to take a closer look at the 486 to see if it could easily be improved in any way. The first thing that could be done was obvious. For various reasons, we wanted to permanently connect two printers to the 486, one a laser printer and the other a dot matrix machine (don’t laugh; dot matrix machines are still good for printing out address labels and multi-part forms). In the past, with the old 386, we had simply swapped printer cables when ever the alternative printer was to be used but that’s a clumsy way of going about things to say the least. Perhaps even more importantly, there’s now a whole raft of non-printer devices designed to run from a parallel port. These include such things as the Snappy video capture system described last month, as well as a huge range of mass storage devices such as Iomega’s Zip and Jazz drives, external CD ROMs and even scanners. The problem is, how do you connect these devices without disconnecting the printer? One solution is to use a printer The existing serial ports were disabled by changing a couple of jumper settings on the multi-I/O card. We also reassigned the existing printer port from LPT1 to LPT2, to avoid a conflict will the “new” printer card. switcher but the most elegant way is to add a second parallel port. That way, both printers (or a printer and some other peripheral) can be permanently connected to the computer and the various applications can be set up to print to a preferred default printer. A quick rummage through our computer junk box soon turned up a dedicated printer card. Just where it originally came from is now a mystery but it proves that if you keep something for long enough, it will eventually come in handy. More to the point, there was no literature with the card and in any case, there are no on-board jumpers to configure. Assuming that it still worked, it would give us our re­quired second printer port. We’ll come back to that shortly. Faster serial ports The other thing that could be done was to improve the performance of the serial ports. As with other machines of its vintage, our 486 used 8250 UARTs (universal asynchronous receiver transmitters) in its serial port circuitry and these are only good for about 9600 Fig.1: to check which type of UARTs your machine has go to the DOS prompt, type msd to run Microsoft Diagnostics and click on Com Ports (or press C). This particular machine uses 16550 UARTs but if yours uses the older 8250s, it will need upgrading to take advantage of the latest fast modems. November 1996  83 baud. Anything faster and you need the later 16550 UARTs. Because our fax/modem is capable of operating at 14.4Kb in fax mode and 28.8Kb in modem mode, we decided that an upgrade would be well worthwhile. The answer of course is to add a new serial card with 16550 UARTs to the motherboard. This time, we weren’t so lucky with our junk box but a quick check in the Dick Smith Electronics catalog soon turned up a suitable RS232 serial card (Cat. X-2233; $39.95). It comes with two 16550 UARTs, two serial port connectors (9-pin and 15-pin) and a manual with all the IRQ (interrupt request) and address configuration details. By the way, you can easily check which type of UARTs your machine has. Just go to the DOS prompt, type msd to run Microsoft Diagnostics and click on Com Ports (or press C). The UARTs used in the computer will be listed at the bottom of the display –see Fig.1. Resolving hardw Installing the hardware Unfortunately, it’s not just a matter of plugging in the new cards and expecting everything to work. If you do that, the existing parallel and serial ports will conflict with the new ones. More precisely, you will get IRQ conflicts and conflicts between memory addresses which could lead to problems. The trick is to reassign one of the parallel ports from LPT1 to LPT2 and to disable the existing serial ports. Before doing that however, we ran Microsoft Diagnostics (type msd at the DOS prompt) to check on the IRQs used by the existing serial ports (COM1 & COM2) and their addresses. This showed that COM1 and COM2 used IRQs 4 and 3 respectively, while their memory addresses were 03F8-03FF and 02F8-02FF respectively. These settings are pretty much standard and a quick check in the manual soon revealed that these were also the default settings on our new serial card. If the latter had been different, it would have been necessary to reconfigure the jumper settings to match the existing ports. For good measure, we also used Microsoft Diagnostics to check on the address and IRQ status of the current parallel port (0378 and 5, respectively). This was mainly a precautionary 84  Silicon Chip Clicking on Computer and then Properties brings up the Computer Properties dialog box below. This lets you view current IRQ assignments and address allocations, so that you can easily choose free resources before adding new hardware. ware conflicts in Win95 Provided you have all Plug and Play (PnP) devices, Windows 95 will successfully allocate resources to avoid device conflicts. The presence of older (legacy) cards can lead to conflicts however, which you’ll need to sort out yourself. To bring up the System Properties dialog box, go to the Control Panel and double-click the System icon. The system properties dialog box will immediately indicate any resource conflicts. To view the resources assigned to a particular item, select it in the System Properties dialog box, click the Properties button and then click the Resources tab. Any device conflicts are indicated in this panel. To change resource settings, deselect Use automatic settings, select the Resource type to be changed (eg, Interrupt Request) and click the Change Setting button. November 1996  85 The two additional cards were inserted into vacant slots above the multi-I/O card. It’s a good idea to remove the connectors for the old COM ports if possible to avoid confusion. If they can’t be removed, label them clearly with a sticker. measure, in case we had to change things later on. Next, we pulled the power plug, removed the back from the PC and pulled the multi-I/O card. In addition to providing one parallel and two serial ports, this particular card also provides two IDE hard disc drive controllers plus two floppy disc drive controllers. Because there was no way of config­ uring the old printer card, the obvious thing to do was to make it LPT1 and reassign the port on the multi-I/O card from LPT1 to LPT2. This simply involved changing one of the jumpers on the card. At the same time, we changed the positions of two other jumpers to disable the serial ports (it really pays to keep the manuals that come with computers). And that’s really all there was to it. We replaced the I/O card, plugged in the additional serial and printer cards, recon­nected everything and found that it all worked. Of course, you have to remember to plug the mouse into one of the new COM ports, since the old COM ports no longer function. In fact, it’s a good idea to remove the old COM port connectors if possible to avoid confusion, or at least label them with a disabled sticker. If you strike trouble, it’s probably due to a resources conflict. To resolve 86  Silicon Chip the problem, check the IRQ settings and the memory addresses carefully and try again. If your printer ports don’t work, for example, try changing the address on one of the cards to the alternative setting. Variations on a theme All the foregoing is just one variation on a number of possible configurations although the basics still apply in each case. For example, a single multi-I/O card could be used to provide both the additional printer port and the new serial ports – just remember to disable the functions that aren’t required on both the new card and the existing card. As a matter of interest, Dick Smith Electronics sell a multiI/O card with four serial ports and three parallel ports (Cat. X-2573) for $129 or you can buy a 2-port parallel printer card (Cat. X-2548) for $49.95. On late-model 486s (and Pentiums), the I/O functions are integrated onto the motherboard but these invariably use 16550 UARTs anyway so you won’t have to upgrade the serial ports. If you do need to disable ports or change address settings, this can be done via the system BIOS. This should only rarely be necessary if adding another printer port, however – in most cases, you will be able to configure the add-in card to avoid conflicts. What about Windows 95? In this case, Windows probably won’t notice the new hardware when it boots and you’ll have to run the Add New Hardware routine from the Control Panel. You can then elect to have Win95 automatically detect the new hardware or, if you are like me and are too impatient to wait through several minutes of hard disc rattling, you can manually select the hard­ware to be added. In the latter case, just say No to the auto-detect routine, then select Ports (COM & LPT) in the next dialog box and finally Communications Port or Printer Port as appropriate. Windows 95 will then assign resources to the new hardware. If these resourc­es conflict with those used by another device, you can change them manually later on – see panel. At least, that’s the theory. We haven’t tried adding an additional printer port on a system running Win95 but the above procedure is routine. Finally, if you have a computer that’s already crammed with multiple disc drives, a network card, a sound card, a SCSI card and any other devices, check your system resources carefully before trying to add more hardware. There are only 16 IRQs avail­able to begin with and over half of these are taken up by essen­ tial items before anything extra is added. Once all the IRQs are gone, that’s it – you can’t add new hardware unless you’re will­ing to sacrifice something SC else.