Product: UM-64 Memory Module
Machines: ZX/TS (not TS2068)
From: Byte-Back Co.
Rt. 3 Box 147 Brodie Rd.
Leesville, SC 29070
803/532-5812
Price: $119.95 Assembled
$109.95 Kit
+$4.95 P&H
Using bigger memories creates opportunities for greater losses in a crash. Byte-Back’s battery-back-up scheme cuts this risk. You’ll also get the possibility to have your operating system in RAM (all but the characters), compatibility with the TS1500, switch-selectable banks in the 8-16K area, an EPROM socket you can switch-select into 8-16K, and reasonable documentation from a company that maintains an evening help line.
When power fails, 6 alkaline batteries (AA size) keep power on your system for up to 30 minutes. These backup batteries supply 9V to the entire system, including other peripherals. Don’t run high-drain items–like a ZX printer–from the backup system. Also, if you’re going to SAVE to tape, you’ll need a battery-powered tape recorder.
You’ll need fresh batteries to get protection with this circuit because the regulator will drop out at 1.22V per cell. Most cells are rated at end-point voltages of 1.1V or less–you can expect about 1/3 rated life in this circuit. The batteries only operate when power fails, so the calendar time can be quite long. SYNTAX recommends testing the backup feature regularly, with non-crucial data.
If you need longer backup times, you can change to a larger battery holder, mounted externally, or modify the circuit to use a rechargeable pack similar to the ones described in SYNTAX (Aug.82 p.5).
Don’t use the Reset function during battery operation. Doing so would wipe out all memory–not just 16-32K. When you lose power, this backup runs your whole system.
With your UM-64, you get MC & instructions to move your operating system into the RAM, where you can modify the code as you wish. Our simple test modified the graphic character codes to make both the 1 & 2 keys print the 1-key graphic–not sophisticated, but enough to see that we really operated from RAM. Changing the character set code in the RAM will not suffice to change the characters, though. The part of your ZX/TS that reads these codes is isolated electronically from the edge-connector where the UM-64 attaches. One use is to change printer USR calls to use LLIST, LPRINT and COPY.
Byte-Back’s UM-64 will work on your TS1500, as well as on the other ZX/TS machines. Of course it doesn’t work on Spectrums or 2068s.
SYNTAX could not get the UM-64, TS1500 and MW-100 printer to function together. By telephone, Jerry Minchey informed us that this is a timing problem for which Byte-Back provides a fix incorporated in later production models than we tested. This fix also allows you to LOAD 32K BASIC programs directly and Jerry will provide it at no charge to people who need it.
In a nice touch, this memory provides two sets of switches to control the 8-16K block. Four of these disable 2K blocks of internal RAM; four control the address of the built-in PROM socket. If your system uses one set configuration, you won’t mind having to open the case to set the switches. SYNTAX constantly reconfigures systems and suggests that you may want to cut a slot in the case.
Documentation includes a parts list, schematic, component layout, and clear directions for use. You also get a clearly stated warranty, a real address, and a phone number.
Construction of this unit uses generally good practice. You will find one piggy-backed IC, a diode, a resistor, and a 3-inch wire that provide a ROM CS function. Also, the battery leads can extend out of the case for your convenience. None of these are, by themselves, bad–but all can cause you trouble in a place with lots of vibration. For most uses, expect no trouble. We like the gold, bifurcated contacts on the connector.