Racal Instruments 3151, Руководство пользователя, Страница: 118 / 136

3151 And 3151A User Manual
Maintenance and Performance Checks 5-20
CPU and VXI ASIC
Checkout
The most important section to be verified after power supply checkout is the
CPU and the VXI ASIC section with its various clocks, address, data lines,
and chip select serial data communication components. Problems with the
digital part could cause erratic operation or erroneous response to word
serial commands.
Problems in the CPU and the digital circuit may cause a complete
malfunction of the entire instrument. The CPU would not start generating
control signals. This makes it impossible to troubleshoot the remaining
circuits. Check the various components associated with the CPU circuitry, its
clocks, and the components associated with the VXI ASIC using the
information given in Table 5-1.
Table 5-1, CPU and VXI Interface Checkout Procedure
Step Test Point Expected Result
1 CPU Clock - U87 pin 19 16 MHz TTL level clock
2 VXI Clock - U109 pin 159 16 MHz TTL level clock
3 ALE - U85 pin 11 Positive going pulses; period 375 ns,
pulse width 120 ns
4 PSEN - U74a and U74b 2.67 MHz TTL level pulses
5 Load a 10000-point wave and perform
the following tests during load time
6 RD - U87 pin 16 Negative going 400 ns width pulses
7 WR - U87 pin 17 Negative going 400 ns width pulses
8 LDACK - U87 pin 5 Negative going 6.5
F
s width pulses
9 ASIC LCS - U104 pin 11 Negative going 6.5
F
s width pulses
10 LR/W - U93 pin 19 Negative going 60
F
s width pulses