Battery backed up 8K to 16K area

[crankorgan]

My meter has a segment stuck on! 4.7 reads 9.7 What a day! I had to bring out my old multi-meter. The ZX81 supply is 4.7 and the proto board supply is 5.1. The supply running the ZX81 is good for three amps. It's a good thing these things are showing up now instead of later.

[sirmorris]

Fooled by the tools

I have to buy a new meter - mine's only good for continuity testing right now

[crankorgan]

I got a circuit running! I used the signal from Pin 6 of the 74HC251 on the Hunter board then buffered on the buffer board. It goes from Low to High whenever there is a Write to the 8K to 16K area. That signal along with a 74HC138-74HC04 and Three 74HC373 gives me 24 output lines. Using a Poke 8192,10240,12288 I see now I can redo the 74HC138 to give me more control signals. Right now I have four 2K apart from 8192. 2K is really 2048 that why the Pokes are weird numbers!

[crankorgan]

Here is the circuit I built on a proto board. It has 24 outputs that can be turned on and off using the command Poke in BASIC.
The circuit can be expanded to one more 74HC273 as it stands. The outputs of the 74HC138 are 2048 apart. So in the 8K to 16K there are only four locations. I use the 8K to 16K signal from the 74HC251 on my Hunter Board. I think it is possible to redo the 74HC138 so it has a location every 1K or even less. This was my starting point!!!! Experiment 1

http://crankorgan.com/EXP-1.bmp

[siggi]

http://crankorgan.com/EXP-1.bmp

Because your address decoder does neither use /MREQ, /RD, /WR, /IORQ for decoding, any matching address during
- PEEK
- IN
- OUT
- REFRESH
- INT-ACK

(not only during POKE) will also trigger your latches and will switch on/off the leds.

Maybe Wilf's description could help

http://www.user.dccnet.com/wrigter/inde ... XRAMIO.htm

Siggi

[crankorgan]

Siggi,
The signal (8k-16K) is derived from a 74HC251 (uses MREQ) that runs the memory on the Hunter unit. The circuit I posted is part of the overall running project. It is not a stand alone project!!!!! As for other circuits on the net they are riddled with mistakes!

John

[PokeMon]

More disturbing I find the offset of the three addresses with 2048 byte which splits your memory block in small pieces.
Why don't you use other addresscoding with ONE block of maybe 8 or 16 addresses.

[crankorgan]

PokeMon,
The Pokes are all in the 8K to 16K area. Once the program is pulled out of the Hunter the area it is free to use. The circuit is for driving Christmas Lights not important data!


John

[crankorgan]

Project Review

1. Build a board that will hold a program for testing and experimenting. Have one hold the program that turns
a ZX81 into a Machine Code Trainer. Done!

http://crankorgan.com/HunterType.bmp

2. Build a buffer board that will protect the ZX81 and allow projects or proto board to sit three feet
away from the ZX81. Done!

http://crankorgan.com/bufferboard1.bmp

3. Build a simple circuit to control lights for testing. Project 1 This could be used to drive Christmas
lights. Done!

http://crankorgan.com/EXP-1.bmp

[PokeMon]

PokeMon,
The Pokes are all in the 8K to 16K area. Once the program is pulled out of the Hunter the area it is free to use. The circuit is for driving Christmas Lights not important data!

I don''t know much about the hunter board but thought maybe you could use this memory area for something else after moving you programs from there.
For additional programs.