BBC Microcomputer Service Manual Oct 1985 Section 1 BBC Micro ...

6.5 Test programs and sample waveforms
6.5.1 Test program
The following program allows you to test the chip select lines of any
of the devices on the computer. It sets up a machine code loop which
accesses the address which you specify as hexadecimal number. Since it
is a closed loop, the only way to escape is to use the break key which
is programmed to re-enter the BASIC program. To escape, enter a zero
address. If you are accessing a slow device, its chip select line
should go low for a full microsecond, but with a fast device, it will
only be low for 500 nanoseconds. In either case, the waveform should be
high for 3 microseconds.
10 *KEY10 OLD|M RUN|M
20 CLS
30 DIM' CODE 20
40 P%=CODE
50 INPUT "ADDRESS",M$
60 M%=EVAL("&" + M$)
70 IF M%=0 THEN END
80 [SEI
90 SEC
100 .again
110 LDA M%
120 BCS again
130 ]
140 CALL CODE
The following is a reproduction of a photograph showing the waveform on
pin 23 of the ADC chip, IC73, when the above test program is running
with address &FECO selected. Scope parameters are 1V/cm, 1us/cm.
44