HP 3457A Service Manual page 204

then checked for accuracy. If the Main Controller finds an error in the returned data, the error
annunciator will flash and executing the AUXERR? command will return a value of 4,
During this procedure, the Main Controller will wait for a response from the A/D Controller. If the
Main Controller never receives a response from the A/D Controller then it will fall into diagnostic 2
and the display will indicate "FAILED".
The data is transmitted in 11 bit frames consisting of one start bit, 8 data bits, one parity bit and one
stop bit. The data is decremented from decimal 16 to decimal 1, with each of the patterns being in-
dependently checked for errors. The A/D Controller remains in the "ECHO BACK" mode until it
receives a decimal 0 data byte. At that time it will execute its 'soft reset' routine. This will set the A/D
Controller to its operational state where it will wait for the Main Controller to direct further activity.
A subset of self test 2 is diagnostic 2 which continuously sends only 4 distinct bytes, FF, OF, 55 and 01
between the A/D Controller and the Main Controller for troubleshooting purposes.
Test 3 is the integrator convergence test on assembly A2/2. This checks the ability of the A/D in-
tegrator (A2US512 and associated circuitry) to run-up from its reference current and then perform the
normal run-down and achieve the predicted result. The Main Controller (ATUSOL) configures the iso-
lated analog hardware (A2U501, A2U101, ete) for 3 volts DC and .0005 power line cycles integration
time, sends the last cal constants generated and opens the input terminal within the A/D hybrid
(A2US5I1) at pin 25.
The A/D Controller (A2U501) initiates a 10uS run-up using a known current, generated by A/D Hybrid
USI1, for a known period of time so the result is predictable. Run-down is executed, results are calcu-
lated and corrected using the last cal constants and the value is passed to the Main Controller for error
checking against the expected results. Figure 8-5 illustrates some of the circuitry used in this test.
On error, if the AUXERR? command is executed, the number 8 will be displayed on the control panel
if their are no other errors. This indicates an "Integrator Convergence Error' (See Table 8-2).
A subset of test 3 is diagnostic 3 which causes the controller to continually loop through Test 3.
Executing DIAGNOSTIC 3 allows monitoring of signals while troubleshooting.
HP 3457A Multimeter
8-39