Hello,
I am working to an expansion board for my CPC 6128 and have some questions about the 'READY' signal (not the one from the floppy).
This signal is drive by the gate array (pin 22) via a 82 ohms resistor.
Is goes then to the Z80 (/WAIT pin 24, enable processor halt), to the LS373 for the data latching on the data bus during the wait and to the expansion connector. So obviously its an output !
Nevertheless I see numerous schematics where this line is (at some time) pulled low by the expansion board so the processor wait sometime for something.
This give a 61 mA current on pin 22 of the gate array if he try to keep this line high during the same time...
I am asking myself if this situation is 'normal' and if it is possible to keep this line low without more check ?
Or if may be the gate array internal design is made so that he never try to give this line high when the Z80 is in wait state ?
More generally how to manage this signal if we want that the processor stay waiting for example during a floating point unit operation.
The fpu give a signal /PAUSE saying when high 'I am ok for a new command' or saying when low 'I am still busy'.
Thanks and regards.
Philippe
The signal is shown on the 464 schematic as an Open Collector output, so the Gate Array is only actively pulling it low. I pressume it's the same on the 6128. Multiple devices can pull it low without harm.
No mention of open collector and pull up resistor on CPC6128 schematic...
Capture.JPG
But could be yes ?
On the 40007, according to the schematic, the output is an open collertor with a internal 600 ohm pull-up.
The 40010 uses a full CMOS buffer. To keep the wired AND functionality, there is a 82Ohm resistor at the 40010 output so you can pull it low with an external device.
The Ready signal is periodic and is low 75% of the time (12 16MHz cycles every 16), so pulling it low will only "short" it for 25%, so an average 15mA.
Note : the ready is only an output. The GA does not care about it.
Very clear !
Thank you.
Philippe
@Wawavoun you are making a maths co-processor, for a CPC?
Cool!
Hi,
I try yes !
Its my first experience of diy for CPC/Z80 so I am in the hard with the address decoding.
See here : https://www.cpcwiki.eu/forum/hardware-related/cpc6128-expansion-board-address-decoding/25/
Hope I will find an explanation of what I see ?
Regards.
Philippe