Search found 211 matches
- Sat Mar 02, 2024 11:06 pm
- Forum: Hardware
- Topic: New open lower RAM module design (photoessay)
- Replies: 98
- Views: 3792
Re: New open lower RAM module design (photoessay)
As for the pure communication protocol, ULA and S80 are masters and RAM is a slave, so the problem with timings is unlikely. Unless ULA is doing something unusual. Unfortunately, knowledge of the ULA communication protocol seems to have been lost to history. Actually, ULA was completely reverse eng...
- Sun Jan 28, 2024 10:15 pm
- Forum: Hardware
- Topic: One spectrum better at loading than another?
- Replies: 9
- Views: 613
Re: One spectrum better at loading than another?
Are they both same issue?
- Sat Jan 27, 2024 10:28 pm
- Forum: Hardware
- Topic: Contended memory with the Z80 in reset
- Replies: 14
- Views: 741
Re: Contended memory with the Z80 in reset
On the other hand, there is EMI from nearby traces, which will drive floating lines as well.
- Sat Jan 27, 2024 7:42 am
- Forum: Hardware
- Topic: Contended memory with the Z80 in reset
- Replies: 14
- Views: 741
Re: Contended memory with the Z80 in reset
When CPU is in reset, it's not driving address lines, so they are floating. Floating inputs change between 0 and 1 randomly.
Try to pull A15 up with 10K resistor
Try to pull A15 up with 10K resistor
- Thu Jan 25, 2024 6:29 am
- Forum: Hardware
- Topic: Could standard cassette use stereo tracks to double data density ?
- Replies: 21
- Views: 1089
Re: Could standard cassette use stereo tracks to double data density ?
Another option is MFM modulation, like in floppies and early hard drives. It would double the speed.
- Tue Dec 12, 2023 1:51 am
- Forum: Hardware
- Topic: Colour clash query
- Replies: 52
- Views: 1715
- Mon Dec 11, 2023 11:10 pm
- Forum: Hardware
- Topic: Colour clash query
- Replies: 52
- Views: 1715
Re: Colour clash query
Memory is one reason. Very first Spectrums only had 16K.
Also, completely eliminating color clash would increase traffic between ULA and lower RAM - more delays for CPU
Also, completely eliminating color clash would increase traffic between ULA and lower RAM - more delays for CPU
- Sat Dec 09, 2023 11:09 pm
- Forum: Hardware
- Topic: Best Spectrum model to get?
- Replies: 24
- Views: 972
Re: Best Spectrum model to get?
LOL8BitSC wrote: ↑Wed Dec 06, 2023 11:14 pm You mean this? http://oldmachinery.blogspot.com/2012/0 ... -mini.html
- Tue Dec 05, 2023 9:41 pm
- Forum: Hardware
- Topic: Best Spectrum model to get?
- Replies: 24
- Views: 972
Re: Best Spectrum model to get?
Toastrack. If you can get it for a reasonable price.
- Fri Dec 01, 2023 10:37 pm
- Forum: Sinclair Miscellaneous
- Topic: Did anyone have the best of both?
- Replies: 11
- Views: 487
Re: Did anyone have the best of both?
I've got 48K Spectrum first.
Later got C64 as well. But the only thing which impressed me was the keyboard
Later got C64 as well. But the only thing which impressed me was the keyboard
- Thu Nov 23, 2023 10:55 pm
- Forum: Hardware
- Topic: RAM chips for lower ram, can these be used?
- Replies: 17
- Views: 510
Re: RAM chips for lower ram, can these be used?
It could be real RAM chips, but (as already mentioned by Mark) may have different access time. Sometimes they are just remarked to put a new date and sell them as "new". People who do it have no clue they are no longer manufactured. Are there any markings on the bottom side? How does the s...
- Wed Nov 22, 2023 6:09 am
- Forum: Hardware
- Topic: Spectrum Diagrom for 27C64 eprom, 8Kb, diy?
- Replies: 20
- Views: 499
Re: Spectrum Diagrom for 27C64 eprom, 8Kb, diy?
Make sure you don't leave unused address pins floating.
Another option is to duplicate ROM image (8KB 4 times or 16KB 2 times) and burn it to fill entire EEPROM.
Another option is to duplicate ROM image (8KB 4 times or 16KB 2 times) and burn it to fill entire EEPROM.
- Mon Nov 20, 2023 10:03 pm
- Forum: Hardware
- Topic: Spectrum black screen with white border
- Replies: 4
- Views: 151
Re: Spectrum black screen with white border
You get it every time on power up?
- Mon Nov 13, 2023 7:47 am
- Forum: Hardware
- Topic: New open lower RAM module design (photoessay)
- Replies: 98
- Views: 3792
Re: New open lower RAM module design (photoessay)
Maybe mark8bit is using different memory on his 2 layer board? And it has different timings?
- Sun Nov 05, 2023 12:55 am
- Forum: Hardware
- Topic: Forcing 128 startup in 48 mode
- Replies: 9
- Views: 352
Re: Forcing 128 startup in 48 mode
Another option. May work on Amstrad models as well.
Cut the trace going to the ROM A14 pin and insert inverter (for example transistor) between the trace and ROM pin. If ROM is socketed, can do it without cutting
Cut the trace going to the ROM A14 pin and insert inverter (for example transistor) between the trace and ROM pin. If ROM is socketed, can do it without cutting
- Sat Nov 04, 2023 11:38 pm
- Forum: Hardware
- Topic: Forcing 128 startup in 48 mode
- Replies: 9
- Views: 352
Re: Forcing 128 startup in 48 mode
I did wonder at the back of my mind if swapping the _Select lines (not sure of the exact wording sorry) between the two IC's would do this, along with probably a couple of other changes. Although vaguely (unrelated) I am reminded of the BBC's ROM sockets where you could simply attach a flying lead ...
- Sat Nov 04, 2023 11:28 pm
- Forum: Hardware
- Topic: Forcing 128 startup in 48 mode
- Replies: 9
- Views: 352
Re: Forcing 128 startup in 48 mode
1. Make your own ROM with 48K ROM starting at address 0. Replace internal ROM with this one. 2. Same but use your own ROM with external ROM interface. Can DIY very cheap 3. Connect A14 pin on the ROM permanently to +5V 4. Remove IC31 (LS174) and replace it with custom board. This board must replicat...
- Thu Nov 02, 2023 3:50 am
- Forum: Hardware
- Topic: What parts can I salvage from an Issue 2 and Issue 4B boards to populate an Issue 3B board?
- Replies: 2
- Views: 119
Re: What parts can I salvage from an Issue 2 and Issue 4B boards to populate an Issue 3B board?
You can use ULA from 4B board in 3B board I believe. But not ULA from issue 2 board.
All ROM and CPU are the same so you can reuse them as well.
All ROM and CPU are the same so you can reuse them as well.
- Sun Oct 22, 2023 6:36 am
- Forum: Hardware
- Topic: New open lower RAM module design (photoessay)
- Replies: 98
- Views: 3792
Re: New open lower RAM module design (photoessay)
One decoupling capacitor might be enough if you have 4 layer pcb with solid ground and power planes. But it's better to have them anyway. It's no fun trying to fix power supply issues.
Capacitors cheap small and easy to solder.
Capacitors cheap small and easy to solder.
- Wed Oct 11, 2023 12:03 am
- Forum: Hardware
- Topic: Pi Pico gate array keyboard interface?
- Replies: 3
- Views: 174
Re: Pi Pico gate array keyboard interface?
Should work.
When no key pressed, you probably need to set your outputs to high-impedance state. Check if Pico supports it
When no key pressed, you probably need to set your outputs to high-impedance state. Check if Pico supports it
- Wed Oct 04, 2023 12:08 am
- Forum: Hardware
- Topic: Noisy audio on +2, but only when RGB is connected
- Replies: 16
- Views: 378
Re: Noisy audio on +2, but only when RGB is connected
When RGB cable is plugged into the DIN socket, the noise is there. When a self-made composite cable (only pins 1 and 2, cut off phono plug and soldered wires to a DIN plug) connected to the DIN socket, there is no noise. When nothing is connected to the DIN socket there is no noise. This means some...
- Sat Sep 09, 2023 1:31 am
- Forum: Hardware
- Topic: Instead of a membrane...
- Replies: 8
- Views: 349
Re: Instead of a membrane...
I remember someone made pcb for real mechanical keys (the standard ones used in PC keyboards) to fit inside 48K rubber case
- Fri Sep 08, 2023 3:14 am
- Forum: Hardware
- Topic: 48k Plus issue 6A - not working - lower RAM?
- Replies: 11
- Views: 386
Re: 48k Plus issue 6A - not working - lower RAM?
That was quick.
Congrats!
Congrats!
- Thu Sep 07, 2023 2:04 am
- Forum: Hardware
- Topic: 48k Plus issue 6A - not working - lower RAM?
- Replies: 11
- Views: 386
Re: 48k Plus issue 6A - not working - lower RAM?
Can you check all the power rails (+5V, +12V and -5V) ? Just do it one by one, by turning the spectrum on for less than one second at a time
- Sat Jul 01, 2023 11:42 pm
- Forum: Hardware
- Topic: ZX Spectrum 128K ULA replacement
- Replies: 17
- Views: 626
Re: ZX Spectrum 128K ULA replacement
Hot ULA is normal. How hot is it?KeplerOfMars wrote: ↑Sat Jul 01, 2023 11:04 pm As the ULA is the only IC that becomes hot over time, I concluded that it is the most likely candidate. Fortunately, I had access to another ULA for testing and the replacement seemed to solve the problem. My machine was certainly not crashing after a few minutes.