I've recently put my hands on a 464 with a 40226 aka pre-asic aka CTRC4, which is also found on the 6128 cost down version.
I did not resist doing some tests regarding :
- Playing with L4N6 pin (to have a 6128 behaviour)
- Extension RAM management compared to 6128 and regular 464
- ROM7 and ROMDIS handling (when in 6128 mode)
Results are :
L4N6 pin
While it is connected to GND on the 6128, it is left unconnected on the 464 and seems to be internally pulled up.
In 464 mode :
- the /ROM2 signal is always high : ROM7 selection is not handled on board.
- the /CAS1 signal is always high : RAM extension is not handled on board.
In 6128 mode :
- the /ROM2 signal is handled on board.
- the /CAS1 is handled on board, with the expected result of getting garbage instead of base RAM when using RAM selection other than C0
- CPC does get stuck after displaying the copyright message and before the "BASIC 1.0" message.
However, plugging a DDI1, even not powered solve the problem. ???
Extension RAM management :
In 464 mode :
- The RAMDIS signal IS taken into account. That mean that extension that does not force the MREQn will work. This include the SymbifaceII
- The C3 mode is NOT supported, as on regular 464.
In 6128 mode :
- Garbage all the way on extension RAM with no extension connected, as expected as no ram is there ;D
- With an extension, C3 is working as expected
- adding 41464 in the alternate footprint and connected to CAS1 instead of CAS0 may transform the 464 in 4128 ;)
ROM7 and ROMDIS in 6128 mode
- Well, no luck. ROMDIS does not prevent internal ROM7 to be selected
- ROMDIS act as an output when ROM7 is selected (However I need to re-check that it is only happening on ROM 7)
- ROMDIS act as the DDI ROMDIS as it is active even during ram access
[attach=2]
Bonus
- on the following page, Gate Array and ASIC Pin-Outs - CPCWiki (http://cpcwiki.eu/index.php/Gate_Array_and_ASIC_Pin-Outs), pin 35 and 36 are undocumented.
- on the PCB in the amendment service manual, these to pins goes to the FDC thru links : pin 35 to DATA, pin 36 to WINDOW
[attach=3]
- Looks like amstrad was designing its own data separator and planned to use it on this version of the CPC. But As hinted in Arnold V specs - CPCWiki (http://www.cpcwiki.eu/index.php/Arnold_V_specs), it was not ready.
Quote from: gerald on 19:28, 02 December 13
- CPC does get stuck after displaying the copyright message and before the "BASIC 1.0" message.
However, plugging a DDI1, even not powered solve the problem. ???
/EXP signal ;)
Quote from: arnoldemu on 19:59, 02 December 13
/EXP signal ;)
Got it ;) .
When the DDI1 extension is not plugged, /EXP is pulled high, and /ROM2 signal is in fact ROM0 and replace the BASIC. As no ROM is connected, it just crash !
Great work. Sounds like it works very similar to the full ASIC used in the plus.
Bryce.
Quote from: gerald on 20:08, 02 December 13
Got it ;) .
When the DDI1 extension is not plugged, /EXP is pulled high, and /ROM2 signal is in fact ROM0 and replace the BASIC. As no ROM is connected, it just crash !
Please "wiki" it.
EDIT: I've wikied it.
Quote from: arnoldemu on 09:51, 03 December 13
Please "wiki" it.
EDIT: I've wikied it.
You are too quick for me ! ;)
Quote from: gerald on 10:06, 03 December 13
You are too quick for me ! ;)
;) if I made any mistakes please correct them. I have copied and pasted your forum posts as close as possible and put your name at the top of the section.
Quote from: gerald on 19:28, 02 December 13The RAMDIS signal IS taken into account. That mean that extension that does not force the MREQn will work.
Thank you for confirming that, has I was not able to get the 464 pre-ASIC[nb]but supposed to work like 464 PLUS[/nb] version for my tests. :)
It can't even do RAM &C3 :o Lightyears off the ASIC or the GA in the 6128 even.
Quote from: TFM on 16:40, 03 December 13
It can't even do RAM &C3 :o Lightyears off the ASIC or the GA in the 6128 even.
According to the posts above: It can't do &C3 in 464 mode (for obvious reasons), but &C3 works fine when it's in 6128 mode.
Bryce.
?? Well, if I have that CPC464 and add 64 KB of RAM: Can it do it then?
Quote from: TFM on 16:58, 03 December 13
?? Well, if I have that CPC464 and add 64 KB of RAM: Can it do it then?
No, unless you take your soldering iron and tie L4N6 to GND.
And /EXP as well ;)
Well, you may not like to read all the time about FutureOS. However if the mouse arrow leaves a smear at the screen, then &C3 doesn't work. If the mouse pointer works well without making traces, then &C3 works. I don't dare to ask you to check that... :-X
Sure, as C3 is only useful for doing double buffering display. ;D
Quote from: TotO on 20:52, 03 December 13
Sure, as C3 is only useful for doing double buffering display. ;D
Double buffering is a very useful function and has saved many mediocre games since the 80's.
Bryce.
Sadly, not enough used on 6128 as I know.
Quote from: TFM on 20:12, 03 December 13
Well, you may not like to read all the time about FutureOS. However if the mouse arrow leaves a smear at the screen, then &C3 doesn't work. If the mouse pointer works well without making traces, then &C3 works. I don't dare to ask you to check that... :-X
Well, FutureOS is not required to check if C3 works or not ;)
But here you are :
Thanks. Result is obvious.