Sinclair ZX80 / ZX81 / Z88 Forums

Because I can produce in a smaller series I can offer a 3-package.
Maybe I can offer a 5-package as well for about 16 GBP.
But to do I want to collect some orders first.

Now I ordered only Prototype version with 5 pieces, resulting price will be GBP 7,00 plus GBP 2,00 postage for an envelope. FIFO order service - first in, first out. Should be delivered this month as promised. Now I found a producer in China for smaller series and I could do a smaller series which w...

OpcodeFetch.jpg As you can see, with this narrowed window on the triggering of the scope, the traces are now clean. Top trace - Data at ROM/RAM 2nd trace - NOP'ed data at CPU (you can clearly see the double NOP when compared to top trace) 3rd trace - RAM CS 4th trace - ROM CS The grid is the same a...

No wonder I had so much trouble pinning down the exact moment to grab the data - this would be so much easier if original ULA is gone & you can determine yourself what happens on the bus, and when. Also these new scope pix seem to suggest that /RAMCS indeed uses /MREQ signal. I don't know where you...

In the picture below you can see RAMCS during video display routine, which is exactly identical to A15 (inverted) or M1, so it's a logical OR with inverted A15 signal. This reflects the problem with executing code in upper memory area above 0x7fff and the so called M1 modification to fix it. The las...

Here I have some scope pictures attached with comments. First I have to say that I was right in my guess, that RAMCS is not set low when MREQ goes low but directly when A15 is high and M1 is low. At least during video display routine (I did not check during normal RAM access). This gives a timing ad...

Tried grabbing bit 0 of the character code on falling edge of T2 (while /M1 and /MREQ are low) - close, but no cigar. Then the rising edge of T2 - again close, but no cigar. Then used 6.5 MHz signal in various ways to try & grab that bit halfway a CPU clock high, or CPU clock low period (yeah I'm a...

For those interested: I used 180 Ohms resistor on CPLD output that carries black/white signal, 330 Ohms on the composite sync output. Other side of those resistors tied together & presto: composite video. Didn't bother to do any exact voltage measurements, but keeping the CPLD's output characterics...

Bill,
if you are not familiar with soldering or electronic components like transistors, you could use this service:

viewtopic.php?t=628
(Option C)

Just put you TS1500 in a box to the post office and wait when it's returned to you.

I'd like a couple of these but 10 may be too many. It does seem like the kind of thing that Rich might sell though - Rich? Fancy a few for SMR?? I'd buy 2 or 3... Yes I know it's maybe many for one person but if I produce same as prototype board I will have only a few with a price of about 10 GBP p...