LED will be on for about 2 seconds to indicate that the stored instrument settings are being ignored. If the RS232 echo mode is on, the sign-on message is sent over the RS232 interface.

Status Byte

The SR510 maintains an 8-bit status register which the user may read to obtain information on the unit's status. The status byte may be read in two ways: by sending the Y command, which returns the value of the byte in ASCII coded decimal, or, when using the GPIB, by performing a serial poll. The returned status byte reflects all of the status conditions which have occurred since the last time the byte was read. After the status byte has been read, it is cleared. Thus, the status byte should be read initially to clear all previous conditions (especially after a power up or after settings have been changed).

The definitions for each bit of the status byte are given below:

Bit 0

Busy. When this bit is set, it indicates the SR510 has unprocessed commands pending on its command queue. For RS232 communications, this bit is always high since the Y command itself will be an unprocessed command. This bit is not reset when read but only when there are no pending commands. Since the SR510 buffers incoming commands, it is not necessary to read this bit before sending each command. Commands received while the SR510 is executing a previous command are stored until all previously received commands have been executed.

Bit 1

Command Parameter Out of Range. This bit is set if a parameter associated with a command is not in the allowed range.

Bit 2

No Reference. This bit is set when no reference input is detected, either because the amplitude is too low or the frequency is out of range.

Bit 3

Unlock. This bit is set when the reference oscillator is not locked to the reference input. If there is no reference input, bit 2 (no reference) will be set but bit 3 (unlock) may not be.

Bit 4

Overload. This bit is set if there is a signal overload. This can happen when the sensitivity is too high, the dynamic reserve is too low, the offset is on, or the expand is on. Overloads on the general purpose A/D inputs or the ratio output are not detected.

Bit 5

Auto Offset Out of Range. This bit is set if the auto offset function cannot zero the output because the output exceeded 1.024X full scale.

Bit 6

SRQ. This bit is high if the SR510 has generated an SRQ on the GPIB interface. This bit is reset after the SR510 has been serial polled. This bit is set only for status reads via a serial poll, ie., Bit 6 always zero for the RS232.

Bit 7

Command Error. This bit is set when an illegal command string is received.

Errors

Whenever a 'parameter out of range' or an 'unrecognized command' error occurs, the appropriate status bits are set and the ERR LED flashes. In addition, any commands remaining on the current command line (up to the next <cr>) are lost. The ERR LED will also light if any of the internal communication buffers overflows. This occurs when 240 characters are pending on the command queue or output queue. The ERR LED will go off as soon as all buffers drop below 200 characters again.

Reset

The Z command resets the unit to its default state. The default front panel settings are listed in the DEFAULTS section of the Guide to Operations. In addition, the interface status returns to LOCAL, the SRQ mask is cleared, the RS232 character WAIT interval is set to 6, and the terminating sequence is reset to the proper defaults.

The command and output buffers are cleared by the Z command. Therefore, it is bad practice to use the Z command before all previous commands have been processed and all responses have been received.

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