The TACT POLBASIC interface replaces the ROM with modified BASIC and offers two OUT ports (data lines ignored): #7F (127) and #BF (191). Only A6, A7, /IORQ, /WR are decoded.
There are also two Jack 3.5mm slots. One connected to the /NMI via diode (is this kind of input?). The second via transistor to one of 7474 outputs, which state can be inverted by an OUT to #7F port (value is ignored).
The #BF (191) port can disable the extrnal EPROM and switch to internal ROM. The NMI button clears 7474 - sets POLBASIC ROM. After
OUT 191,0 you need to make reset to make the internal BASIC to work (perhaps because of extra variables set by POLBASIC ROM). Then NMI switches back to POLBASIC ROM and OUT 191,0 again to internal ROM with no need for reset anymore.
Note to schematics: in original, pin 3 of 7410 is not connected, what occasionally can cause problem.
Files for download
- tsrv32.zip 56.0kB (2006-03-29 05:21)
- The board documented in Eagle files, made from a working item.
- tsrv32l.jpg 59.8kB (2004-02-05 20:54)
- Board picture - bottom side.
- tsrv32e.jpg 55.8kB (2004-02-05 20:42)
- Board picture - elements side.
- tsrv32s.png 36.2kB (2004-02-01 17:28)
- Schematics (Eagle picture).
- tsrv32b.png 26.7kB (2004-02-01 17:29)
- Board (Eagle picture).
- polbasic.zip 13.0kB (2004-01-31 17:04)
- The POLBASIC ROM replacement.
- 128KB - 512KB PEROM - FlashD0
- 128KB or 512KB PEROM (or Flash EPROM) for Spectrum compatibile computers. Can support 4MB RAM upgrade and be base for ZXVGS installation.