andykmv
Active member
the 8080 datasheets dont give me enough information on the functioning of the HOLD and READY signals and their effect on the CPU.
context: SI clone pcb doesnt boot properly. i noticed a few of the signals into the CPU were in a steady state (not toggling) and, I also noticed that the CPU databus pins (D0-D7) look to be in HiZ state - i will have to confirm if the steady signals were the the HOLD and/or READY signals.
related posts:
http://forums.arcade-museum.com/show...19&postcount=1
http://forums.arcade-museum.com/showpost.php?p=1616786&postcount=1
the questions i have in mind are:
1. READY/WAIT (CPU pins 23, 24)
this signal comes from a 74ls74 location E3 pin 9, on the Midway SI schematic/layout, C1 pin 9 on the GW layout.
Q: if the READY line is held LOW does this effectively halt the cpu ? - does this put the databus in HiZ ?
2. HOLD/HLDA (pins 13,21)
this signal comes from a 74ls86? location A4 pin 3, on the Midway SI schematic/layout.
if the HOLD line is held HIGH does this effectively halt the cpu ?
- the datasheet suggests this does put the databus in HiZ under certain conditions.
context: SI clone pcb doesnt boot properly. i noticed a few of the signals into the CPU were in a steady state (not toggling) and, I also noticed that the CPU databus pins (D0-D7) look to be in HiZ state - i will have to confirm if the steady signals were the the HOLD and/or READY signals.
related posts:
http://forums.arcade-museum.com/show...19&postcount=1
http://forums.arcade-museum.com/showpost.php?p=1616786&postcount=1
the questions i have in mind are:
1. READY/WAIT (CPU pins 23, 24)
this signal comes from a 74ls74 location E3 pin 9, on the Midway SI schematic/layout, C1 pin 9 on the GW layout.
Q: if the READY line is held LOW does this effectively halt the cpu ? - does this put the databus in HiZ ?
2. HOLD/HLDA (pins 13,21)
this signal comes from a 74ls86? location A4 pin 3, on the Midway SI schematic/layout.
if the HOLD line is held HIGH does this effectively halt the cpu ?
- the datasheet suggests this does put the databus in HiZ under certain conditions.
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