Working on a stack of these boards. There is no watch dog disable but it is an easy enough thing to do by removing Q10 (the WD then can't toggle reset). With the Fluke connected I can run UUT and game will run fine I can test the Video Dram from 0x4000-0x7FFF no problem. I can test the cpu SRam from 0xD080-0xDFFF no problem. The cpu SRam from 0xD000-0xD07F though give a data error when trying to write to it.
From the mame memory map it shows that ram 0xD000-0xD03F is protected_ram (I think this is a typo because it is blocked for me to 7F).
Looking though the tech tools list history I saw mention from Kev in 2004 that there is a section of the ram that has a latch attached to reset. I think that is the protected ram mentioned in the memory map. The map also says address 0xA55B controls the protection. Looking at the gorf schematic page 63 (the rom/ram board) I can see the latch Kev mentioned. U9:11 (74LS74) controls the chip select for X21 / X22. And this is tied to reset so would clear if the WD were to kick (but I have disabled it) This is in turn fed by U10:9 (74LS133) which takes in a bunch of address / control lines and's them and inverts. So if anything isn't set it will output false. One of those intputs (pin 4) is from U16:13 a MC14078 (8 input NOR). Ensuring that a bunch of other things are not set which gives us a enable latch of A55B. Problem I am having is one of the inputs to U16 is pin 5 which it IORQ!. When I try to write to A55B with fluke to latch that the memory protect, IORQ! Is always high. So U16:13 is low, which make U10 fail the and. I verified IORQ! Is working (I can run the UUT) and see it toggle. Reading the spec's on the Z80 control signals I think that should be pulled low whenever the CPU is doing a write. But it's not when doing so from the fluke. I could jumper U10:4 to ground in some manner but would rather understand what is happening. Ideas? Thanks, David _______________________________________________ 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/