4 Nov
2011
4 Nov
'11
1:20 a.m.
John Robertson wrote:
I hadn't considered minimum clock speed as a
factor.
The 3851 maximum clock period is 10 us (i.e., minimum clock frequency
100 kHz). I think I was probably running the 6511Q at 2 MHz. (Maybe it
was a 6511AQ.) I probably wasn't actually meeting the 3851 maximum
clock period spec; I don't remember what the actual timing ended up at.
At 5V and room temperature, the part will probably operate OK to a fair
bit slower than the spec.
Fortunately I have what appears to be the same code in
the two
3851s as in the redesigned 3870 board so reading those should
give me useful code (perhaps with slight address massaging) to
work in the 38P70 test CPU. Then on to designing a replacement
for the 3870 once I have good code!
Bear in mind that the timer in the 3851 works differently than the timer
in the 3870 series, so any code using the timer may not be portable
between the two. The 3851 timer is a twisted ring counter, so it
doesn't count in normal sequential binary. The count sequence is given
in the documentation. The 3870 counter is a binary counter.