Fluke 45 - Main Processor Timing

45
Service Manual
5-16
E
2.4V
AD
t
0.8V
PW
PW
PW
t
cyc
EL
EH
tt
t
t
t
t
t
t
tt
t
t
t
Ef
AH1
2.4V
0.8V
AH2
HRW
RW
2.4V
0.8V
t
RWD
DDW
HW2
HW1
2.4V
0.8V
DSR
ACC
HR
HLR
DLR
2.0V
0.8V
0.8V
A0
~
R/W
RD,WR
MCU Read
MCU Write
D
0
~
D7
D
0
~
D7
LIR
A15
,
Er
qb24f.eps
Figure 5-3. Main Processor Timing
To check the ROM decode circuitry, verify that A1U9-6 is transitioning low and that
these transitions correspond roughly to the low-going transitions of LIR*. Pin 6 must be
low when LIR* is low; see Figure 5-3. Verify that this signal also appears at the ROM
Chip Enable, A1U8-20. If the ROM Chip Enable is present, the problem is with the
ROM itself or there is a fault in the address/data lines among the 6303Y Main Processor,
ROM, RAM, and IEEE option connector.
If SWR1 (A1U6-21) and SWR2 (A1U6-22) transition low, but SWR3 (A1U6-23)
remains high, the problem is with the RAM decode circuitry (A1U9), the external RAM
(A1U10), or the address/data/control lines between the RAM and the 6303Y Main
Processor.
To check the RAM decode circuitry, verify that A1U9-8 is transitioning low and that
these transitions correspond approximately to the low-going transitions of WR* (A1U6-
66). It may be necessary to continually reset (power on) the meter to check these lines,
since the activity probably halts quickly when the meter software goes awry. Verify that
the signal on A1U9-8 also appears at the RAM Chip Enable, A1U10-20. If the RAM