steve@anasazi.UUCP (Steve Villee) (05/06/86)
I asked these questions on Compuserve and got no response. Let's see
what happens on Usenet.
I'm thinking of upgrading the RAM on my Macintosh to at least 1 megabyte,
and possibly up to 4 megabytes. As I see it, there are two basic approaches:
(a) send the /RAS signal to only one bank of 512K at a time, based on the
new address lines, or (b) send the /RAS signal to all the banks, but send
upper and lower /CAS to only the selected bank. Approach (a) draws less
power, but it may exceed the refresh timing margins. Also, there are
rumors that the some of the address lines (such as the video address lines)
are not valid for the entire time /RAS is active, and so the address lines
that will be used for bank selecting must be latched when /RAS goes active.
If this is true (I find it a little hard to believe), then approach (b)
will be simpler to implement.
My questions: Is it true that some of the address lines are not valid
throughout /RAS? Which approach is actually used by commercial third
party upgraders? How much extra power can be drawn without exceeding
the limits of the Mac power supply (ignoring heat dissipation)? In a RAM
access cycle of the Timing State Machine (TSM), how many nanoseconds elapse
between /RAS (pin 14) going active and /COL (pin 18) going active? Between
/COL and the appropriate /CAS lines (pins 12 and 13) going active?
Thanks for any information.
--- Steve Villee; UUCP: ihnp4!terak!anasazi!steve; CIS: 72447,3564
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