Search found 45 matches
- Tue May 07, 2024 12:07 pm
- Forum: Hardware
- Topic: uLA81 pin problem
- Replies: 4
- Views: 389
Re: uLA81 pin problem
I assume this is what you are looking for: https://www.reichelt.de/stiftleiste-rm-2-54mm-gerade-1-reihig-40-polig-w-p-952-12-040-1-p331061.html?CCOUNTRY=445&LANGUAGE=de&trstct=pos_0&nbc=1&&r=1 Available from W-P in different length (of pins) and number of pins. Seems to fit into IC sockets. Regards ...
- Thu May 02, 2024 8:03 am
- Forum: Hardware
- Topic: SCHEMA interface memotech I/F centronic type parallel printer interface
- Replies: 3
- Views: 609
Re: SCHEMA interface memotech I/F centronic type parallel printer interface
Interesting Interface. Schematic can be found in the German forum: https://forum.tlienhard.com/phpBB3/viewtopic.php?t=4628 Content of EPROM and typ of PAL (PAL16L8-4CN) can be found here, as well as a picture of one (parts) side of the PCB: https://www.sinclairzxworld.com/viewtopic.php?f=8&t=3831 To...
- Thu Mar 16, 2023 10:32 pm
- Forum: Development
- Topic: Using an external EPROM
- Replies: 5
- Views: 1534
Re: Using an external EPROM
Might be, this is doing what you want:
https://ws-nbg.de/zx81/main.php
https://ws-nbg.de/zx81/main.php
- Thu Mar 16, 2023 9:02 pm
- Forum: Development
- Topic: Using an external EPROM
- Replies: 5
- Views: 1534
Re: Using an external EPROM
It takes a lot of effort to display characters from external ROM.
If characters in internal and external ROM are the same and at the same locations you can enable internal ROM in refresh cycle and external ROM in all other states.
If characters in internal and external ROM are the same and at the same locations you can enable internal ROM in refresh cycle and external ROM in all other states.
- Fri Feb 17, 2023 10:51 pm
- Forum: Hardware
- Topic: The reason native hi-res is only possible on the 1k zx81??
- Replies: 8
- Views: 1673
Re: The reason native hi-res is only possible on the 1k zx81??
There is UDG and CHR$128 HRG. Most of the internal and external memory expansions do not support that.
External a UDG4ZXPAND module is needed in addition to memory expansion.
Internal there is quicksilva UDG board.
- Fri Feb 17, 2023 6:56 pm
- Forum: Hardware
- Topic: The reason native hi-res is only possible on the 1k zx81??
- Replies: 8
- Views: 1673
Re: The reason native hi-res is only possible on the 1k zx81??
With some additional logic internal 1k can be mapped at 8k-16k.
I also heard that one of the printer interfaces uses internal 1k to patch ROM.
I also heard that one of the printer interfaces uses internal 1k to patch ROM.
- Fri Feb 17, 2023 7:00 am
- Forum: Hardware
- Topic: The reason native hi-res is only possible on the 1k zx81??
- Replies: 8
- Views: 1673
Re: The reason native hi-res is only possible on the 1k zx81??
The other point, is that some modern SRAM chips are too fast at responding to the control signals, and hence this messes up the timing. Mark This can be fixed by delaying /RAMCS using a capacitor, https://www.sinclairzxworld.com/viewtopic.php?f=7&t=2120 adding some non inverting gates between /RAMC...
- Thu Feb 16, 2023 10:06 pm
- Forum: Hardware
- Topic: ZX81 Hi-Res
- Replies: 40
- Views: 14717
Re: ZX81 Hi-Res
If I understood right, this is a classical race condition. ULA load shift register at the falling edge of T4 cycle. /MREQ go to high at the same time. So this is working with the original slow ROM and very slow RAM. With fast RAM the data is invalid prior ULA is reading it. So you need to delay /RAM...
Re: CHR$X16
I was able to build an internal CHR$16 / CHR$128 mod. There is no PCB, just soldered a RAM on the back of the ROM and build a small dot pcb. https://sinclairzxworld.com/viewtopic.php?p=37302#p37302 This need at least 8-16k range not used by external RAM. I can tell in more detail if needed. I also h...
- Wed Nov 11, 2020 5:57 pm
- Forum: Development
- Topic: ZX81 Clone Tynemouth Minstrel 3
- Replies: 48
- Views: 36955
Re: ZX81 Clone Tynemouth Minstrel 3
Be aware that 74HC logic need 3,5V as minimum high level. TTL logic as used in the original ZX81 need only 2V as minimum high level. I struggled with this issue as well when I build my Minstrel. I found four working solutions: - Replace all HC chips by HCT (this will cause some other issues with RC ...