Micro­power

  

April 1982, Volume 2, Number 2











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must be bent sideways so that they miss the socket, and can be wired to the Bank Select board. Data bit BS2 and its complement are gated with E000-FFFF from the MD PROM in a quad OR gate, 74LS32. A logic 0 on BS2 will select XROM and hence the EPROM block, and a logic 1 will select the Basic ROM (BROM). The CLR input of the 74LS175 is wired to the system RESET line, ensuring that bank 0 is selected on reset or power-up.

Wiring of the link blocks LKB1 – LKB8 is shown in figure 2. Addresses A10 and A11 are wired from the workspace RAM linkblock, LKB9. Link switches LSW1/7 and LSW1/8 should be up. Note that the wiring scheme shown is only suitable for 2732s; Texas 2532s do not have the same pinout.

Fig. 2 LINK BLOCK WIRING FOR 2732 EPROMS

One further complication of this method of bank selection is that the addresses E000-EFFFH are confined to EPROM block A, and addresses F000- FFFFH are in block B. This is best explained by the table bellow: E000-EFFF F000-FFFF Bank 0 A1 (IC35) B5 (IC39) Bank 1 A2 (IC36) B6 (IC40) Bank 2 A3 (IC37) B7 (IC41) Bank 3 A4 (IC38) B8 (IC42)

My own system Jumps to D000H on reset, where a menu display and control program select the required bank and execute at the appropriate address. Software intended for execution in RAM is copied down to 1000H by the control program.

Figure 3 shows a suitable vero layout for the bank selection unit. The unit is shown from the component side.


This is an OCR’d version of the scanned page and likely contains recognition errors.











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