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AST RESEARCH TECHNICAL BULLETIN TB-0143 1-15-86
TWO SIXPAKPLUS CLOCK CHIPS
Recently, the clock chip on the SixPakPlus has been changed to a
different vendor. The latest version of the SixPakPlus utilizes
a Ricoh RP5C15, as opposed to the earlier versions of the
SixPakPlus using a National Semiconductor part number MM58167.
Since this change has taken place, the question has been raised
as to how the ASTCLOCK.COM program (included with SuperPak
Version 4.3) can tell the difference between these two chips.
Internal address "D" is used by ASTCLOCK to determine which chip
is being used. The address was chosen for the following reasons.
For the Ricoh clock chip, this address is a "read-only" address;
it ALWAYS returns a "0" when read. The same address for the
National Semicoductor chip is RAM and will read back whatever is
written to it.
So ASTCLOCK writes a "1" to address D, bit one. If the result is
a "0", the program knows a Ricoh chip is present and goes to the
appropriate place within the program to read this chip.
Conversely, if a "1" is read back by ASTCLCOK, then the program
knows to use the portion of the clock dedicated to the National
Semiconductor chip.