Borer Data Line Driver

The second of the modems from the original Comms Room installation and a marked improvement on the previous Borer modem. This still features a metal case, but is probably about a third of the size of the 2400L discussed previously. One significant improvement, apart from the size, is that this modem could be run at various data rates, ranging from 600bps to a whopping 19200bps.

Again, this would have provided remote access to the IBM 7171 controller.

Like the previous Borer modem, this device had the same light blue cover and a black front, tho’ in this case, it is not easily removeable. A similar array of LEDs adorn the front, with indicators for DCD, RTS and both TX and RX. In addition, buttons are provided in order to apply loopback tests on the line, either local or remote and these also contributed to common issues in that old environment, where test buttons were accidentally latched when other work was being carried out on another piece of kit. Still, these were an easy fix;-) One further adornment is a thumbwheel accessible from a hole in the front, which was used to set the device’s data rate.

Around the back, along with the line terminator and serial connector, is a nice little table which shows the data rates available with this device. This also shows that this could run either asynchronously (presumably taking the line speed from the speed of the data on the serial interface) or synchronously. One hint as to the actual speed that this device provided to the end user is that the thumbwheel on the front, is set to position 4 which corresponds to 4800 Synch on the table. As I do not recall ever changing this in all the years this has been in the loft, and both modems I have are set the same, it is safe to presume that this did, indeed, run at 4800bps. What lucky folks those users were;-)

Again we see that the line termination was done using screw-terminals. It wasn’t until theses devices were replaced that we started using RJ11 cables to connect modems to BT lines, although some BT lines were actually presented this way, the modem technology lagged a little way behind.

As with the previous Borer modem, I possess a working pair of these and the glowing LEDs of one them appear in the header graphic on the site:-)

Micom-Borer 2400L

The first of a couple of posts featuring modems that used to reside on the home-made shelving ‘rack’ in the Comms Room. A monstrous unit, with a metal case so rather on the heavy side, and whose size defies its dimunitive 2400bps data speed. This would have been used to provide access to the mainframe via the 7171 controller for remote sites. At the other end of this would have been either an IBM or Memorex CRT VDU. Green-screen, natch.

Looking at the front of this, we see a dark front cover, behind which are a series of LEDs to indicate the state of the carrier, the RTS/CTS signals and the TX and RX of data. There is also a test LED, which would indicate that the unit was in test mode. This was set by a toggling a dip-switch that is revealed when the front cover is removed.

At the back, we see two V24 D-sub connectors, one for the digital I/O, and one Auxilary. This latter could have been used for a printer, I presume, but I don’t recall us ever running remote printing via these modems. Printing, if any, would have been to a printer connected directly to the VDU. In addition, there is a screw terminal for connecting the to the BT line. If we were lucky, someone (and I’m looking at you Adrian) would have actually put terminating lugs on the end of the end cable, but usually the ends of the cable were just wrapped (or not) around the posts before the screw was tightened.

The modem at the Comms Room end would have its serial port connected directly to the IBM 7171 controller and the remote modem would have the VDU connected to its corresponding serial interface. If you think that this was just one of about 20 or 30 modems ‘installed’ on the racking, then you may be able to imagine the mess that resided at the back of the old rack, with each modem having its mains, serial and line cables coming out the back and trailling off to who knows where!

Incidentally, I have a pair of these monsters, both of which still function.