Battery backed up 8K to 16K area

[crankorgan]

Today I tested the Data Buffer (7HC245). OE needs to be LOW and DIR needs to be high and the DATA lines then appear on the output of the 74HC245. So that concludes the Hunter/Buffer unit. Now I have to decide what project to build that plugs into the unit. A simple sound card? or A unit that drives Christmas lights? I located the BB1 schematic here on this forum. That unit can take in signals and control relays.

http://www.megaupload.com/?d=C6AFJ7H0

[1024MAK]

Are you going to use Z80 I/O addressing or are you going to use memory mapped addressing (so that PEEK and POKE can be used)?

One of the annoying things about computers and hex is that different systems use different symbols to represent hex
When I first saw things like 0x56 I was confused Now I know that this is how hex is often represented in the "C" programming language and this practice seems to have spread far and wide.

Keep at it, you are doing well
I always look forward to your posts

Mark

[crankorgan]

It looks like the first experiment will be with a 74HC138, 74HC273, 74HC00 and some LEDs. When I build, I try to use standardized concepts. I have several circuits to borrow from. I am also trying to use chips I already have. I bought a controller years ago that sent movies to the rooms in a hotel. It controlled 8 VCRs. It was all wire wrapped 74HC logic chips. The parts have become several project over the years. I like building and documenting what I have done! I used to hate writing! Now I have to build and write something every day. I am also hooked on long walks. I hope this adventure helps others. It seems people buy a ZX81 and then add memory. Then they fix the video. Then maybe the keyboard. Hopefully this adventure will inspire others! Years ago I piggy backed a 8255 or an other chip on my Z80 processor chip. I was able to control LEDs. Then Sync magazine went under and my ZX81 gave way to cable decoders. Once I get LEDs to blink I will have gone further than before!!! Since I now have battery backed up program capabilities.

[crankorgan]

1024Mak,
I am going to use Memory Map. This way my program in BASIC will be easy to follow using just POKE statements. I have been using FOR I= 1 TO 1000 for delays. I see there is a PAUSE statement. If the winter becomes long and bleak then I can get into other experiments. At this point there are lots of things to try!!!!

John

[crankorgan]

AY ! CARAMBA In order to use a simple BASIC program the circuit has to be memory mapped. A combination of Gate and 74HC138. I have to check my IBM notes. I have a simple circuit somewhere!

[crankorgan]

I just woke up! It's 2AM! I just realized I have a 74HC251decoder on the Hunter section of the project. It puts out a LOW between 8192 to 16384. I should be able to use this along with some gates or a 74HC138 to produce my Memory Mapped address. Back to sleep!

[crankorgan]

I am going to use my proto board for this experiment. The 74HC251 will supply a High to a 74HC30 at 8192 to 16384. Other address lines will go through 74HC02 chips to provide the other signals to the 74HC30. So at 8192 and only at 8192 the output of the 74HC30 will go LOW and enable my Data Out Chip. A WR signal will then pop out the data. (Hopefully) Out for a Walk!

[crankorgan]

My 35 year old Proto Board station hooked to my ZX81 VIA the Buffer Board. The connectors that I made from IC sockets on the buffer take the telephone wire without solder!!!!

http://crankorgan.com/exp1.jpg

The buffer board allows the use of long wires between the ZX81 and project. You can move wires on the proto board and it will not lockup the computer. The Hunter section can hold the test program during power down. This is incredible! for a experimenter.


I tried using the signal from the 74HC251 along with some gates. No go! What I did find is I could use the pin 6 signal from the 8K to 16K decoder (74HC251) as a clock. So I am able to control lights with just a 74HC273. I have been working with 74HC chips. I might have a few 74LS27 chips to build a address decoder. I tried using a 74HC30 and two 74HC02 chips and the signal from the 74HC251. All the signal are pulsing in the right direction.

[sirmorris]

Looking good

[crankorgan]

I ordered some 74HC27 chips and some 74HC259. After I clean up I will add a second 74HC273 to the first. I am thinking of chaining several chips. The output of one goes into an other. The same clock chip drives them. So a binary number gets shifted over as a new number comes in.