I am getting the following readings on the CPU:
Pin 17??High
Pin 18??High
Pin 23??Low
Pin 24??Low
Pin 25??Low
U45 C
Pin 5???pulses H and L
Pin 6???L
Pin 4???pulses H and L
U45 A
Pin 2???L
Pin 3???pulses H and L
Pin 1? ?L?? ?--->?Goes to U17 pin 24
U45 B
Pin 8? ??L
Pin 9? ??L
Pin 10??L?? ?--->?Goes to U17 pin 25 ?
? ? ? ? ? ? ? ? ? ? ? ? ?and?23
I thought U45 was defective so I replaced it but I got the same readings after installing a new IC.?
Pin 5 of U45 comes from the timer IRQ.??Is it normal for the voltage to pulse from high to low and back???
Thanks for any inputs.?
Joey
On Saturday, February 20, 2021, 10:42 PM, mjkirk12 via groups.io <mjkirk12@...> wrote:
Yes, these all should normally be high.
Pin 17 HALT* must be high (stops CPU when low)
Pin 18 RESET* must pulse low to reset CPU.? ?(stops CPU if held low)
Pins 23-25 should normally be high, but with interrupt event (UART/TIMER), could be low
Other pins (need scope)
14, 49? Vdd? = +5V DC for CPU power
15 CLK must have a 10 MHz clock
20 E - should have clock signal at 1 MHz.? ? A single period of clock E consists of 10 MC68000 CLK periods (six low, four high).
9? R/W*? - read/write should be toggling high/low
6 AS*? - address strobe should be toggling high/low
Most data and address bus lines should all toggle high/low as well - showing activity of CPU.
More info:
