ameyer@nsscb.UUCP (Andy Meyer) (10/28/88)
I am trying to read the realtime clock on an Altos 5-15ad under CP/M.
The documentation only tells me it's channel 3 of a Z80 CTC, and I have
no information on how to read/update this chip. Does it have registers?
Has anyone got this machine? It runs CP/M and MP/M (3 users) and can fit
700k on a 5.25" floppy!
ADVthanksANCE
Andy
==-- Andreas Meyer, N2FYE
-====--- AT&T National Systems Support Center
--==---- South Plainfield, NJ
---- uucp: ..!rutgers!psuvax1!nsscb!ameyerrlb@xanth.cs.odu.edu (Robert Lee Bailey) (10/29/88)
In article <538@nsscb.UUCP> ameyer@nsscb.UUCP (Andy Meyer) writes: >I am trying to read the realtime clock on an Altos 5-15ad under CP/M. >The documentation only tells me it's channel 3 of a Z80 CTC, and I have >no information on how to read/update this chip. Does it have registers? I'm not familiar with the Altos, but, I am familiar with the Z-80 CTC. The Z-80 CTC has 4 independent counter/timer channels. Each is individually programmable. In the counter mode, a value is loaded into the CTC, which then counts down to zero and generates an interrupt(one time only). In the timer mode, a value is loaded into the CTC, which then counts down to zero, generates an interrupt, and then starts over again (the interrupt occurs repeatedly). The bottom line is that you need to know what the interrupt vector is for the CTC. That is the location of the routine that is executed when an interrupt occurs. I have a Xerox 820 which uses the CTC to generate an interrupt once each second to perform a real-time clock function. The CTC interrupt handler gains control after each interrupt. This routine then increments a memory location, checks to see when it reaches 60 (secs), resets that location to zero, and increments the minute address, etc. If you have the source to your BIOS, you may find the answer as to where your interrupt vector is located. If not, you may be able to find the address(es) that are being incremented on each interrupt by using DDT to dump sections of memory. Just repeatedly dump the same area and look for one or more addresses that are being incremented once each second. When you have found the address, you can then write a routine to examine the addresses and get the current time value. I hope that this is of some help, although I realize it may be somewhat vague. Bob Bailey