On Fri, Mar 18, 2016 at 11:27 AM, John Robertson <jrr@flippers.com> wrote:
These only work with CPUs that can support having their address and data lines floated when you select a particular CPU pin, AND that pin MUST have a pullup resistor on the UUT PCB. In some cases that pin was simply wired to Vcc, and then to able to use the 90 you have to cut the Vcc trace and add a 10K pullup.
The 90 works by cycle stealing, it runs when the CPU is on the opposite cycle. Rather cute in fact - the game can be running and you can run a RAM, ROM and I/O test at the same time!
thanks for posting this technical info John, much appreciated! _______________________________________________ Techtoolslist mailing list Techtoolslist@flippers.com https://pairlist7.pair.net/mailman/listinfo/techtoolslist FTP site is: ftp://ttl.arcadetech.org/TTL/Test_Equipment Archive site: http://seven.pairlist.net/pipermail/techtoolslist/