Search found 1723 matches

by 1024MAK
Wed Oct 18, 2017 11:56 pm
Forum: Hardware
Topic: ADDRESSING RAM AT 16K+
Replies: 7
Views: 95

Re: ADDRESSING RAM AT 16K+

If this schematic is accurate, there is ROMCS and A14 on ULA. So how does the ULA react when A14 is high with regards to ROMCS (assuming CPU has MEMRQ active... I am expecting that ROMCS is an output and A14 is an "input" to ULA "asking ULA" to enable ROM. So, returning to this, with respect to the...
by 1024MAK
Wed Oct 18, 2017 6:47 pm
Forum: Sinclair Misc
Topic: Get a LIFE?
Replies: 5
Views: 92

Re: Get a LIFE?

mhudson52 wrote:
Wed Oct 18, 2017 6:45 pm
I've searched all over and have yet to see a "New Posts" button to click. What am I missing?
It's in a drop down list, click "Quick links" which is in the top left of every page.
IMG_5458.JPG
Quick links drop down list
IMG_5458.JPG (200.95 KiB) Viewed 29 times
Mark
by 1024MAK
Wed Oct 18, 2017 6:04 pm
Forum: Hardware
Topic: ADDRESSING RAM AT 16K+
Replies: 7
Views: 95

Re: ADDRESSING RAM AT 16K+

If you look at this schematic (where some errors have been corrected, ignore the French video circuitry) which shows the edge-connector connection points (the X's in square boxes), it may help. http://fetrmartin.free.fr/ZX81/schema_ZX81_Fr.gif Both /ROMCS and /RAMCS have series resistors between the...
by 1024MAK
Wed Oct 18, 2017 3:13 pm
Forum: Hardware
Topic: ADDRESSING RAM AT 16K+
Replies: 7
Views: 95

Re: ADDRESSING RAM AT 16K+

sirmorris wrote:
Wed Oct 18, 2017 11:26 am
That's the best explanation I've seen Mark :ugeek:
Thank you :D

Mark
by 1024MAK
Wed Oct 18, 2017 9:58 am
Forum: Hardware
Topic: ADDRESSING RAM AT 16K+
Replies: 7
Views: 95

Re: ADDRESSING RAM AT 16K+

Oh, and external RAM memory expansions have their own address decoder circuitry, so force the ZX81 /RAMCS ( or RAM /CS) line to logic 1 (high) to disable the ZX81's on board RAM. But because the external RAM memory expansions have a similar "incomplete" address decoder, a 16k RAM expansion will appe...
by 1024MAK
Wed Oct 18, 2017 9:38 am
Forum: Hardware
Topic: ADDRESSING RAM AT 16K+
Replies: 7
Views: 95

Re: ADDRESSING RAM AT 16K+

The ULA only uses address line A14 (and the Z80 CPU control line /MREQ) to decode the control signals for the ROM and RAM. You have to look at the address in binary: ROM RAM Bit: 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 /CS /CS ==================================================== === === ROM X 0 X X X ...
by 1024MAK
Sun Oct 15, 2017 10:53 am
Forum: Sinclair Misc
Topic: MEMOTECH
Replies: 15
Views: 259

Re: MEMOTECH

My post above updated :mrgreen:
by 1024MAK
Sun Oct 15, 2017 10:18 am
Forum: Sinclair Misc
Topic: MEMOTECH
Replies: 15
Views: 259

Re: MEMOTECH

You can often find out more if a patent is still active. https://www.gov.uk/search-for-patent As Paul says, unless someone is actively taking care of the rights, most would have expired. Except for copyright which will still be in force. The original Memotech company went into receivership after poo...
by 1024MAK
Sat Oct 14, 2017 7:02 am
Forum: Hardware
Topic: What is the going price to have EPROMs burnt?
Replies: 14
Views: 185

Re: What is the going price to have EPROMs burnt?

Depending on the actual type of HDD, it pay be worthwhile checking to see if there is access to apply a single small drop of fine oil for the motor/drive bearings.

Mark
by 1024MAK
Fri Oct 13, 2017 8:59 am
Forum: Hardware
Topic: ZX81 rebuild
Replies: 36
Views: 818

Re: ZX81 rebuild

gozzo wrote:
Fri Oct 13, 2017 3:00 am
oh, what were these eeproms that were bad? and from what supplier? i've bought a fair few but not got round to using them yet...
Read through this thread over on StarDot.

Mark