ICS ELECTRONICS 4809A, Instruction Manual

Page: 59 / 131

3-8
3
The Modbus Error Register reports a decimal value of the last error detected
with the Modbus message transmission or reported back from the Modbus
slave device. This register is cleared when read by the Modbus E? command.
The *CLS and *RST commands have no affect on this register. Refer to
Table 3-5 for the Modbus Error Register values. The following commands
will generate a Service Request when a Modbus error occurs:
*ESE 64 ‘enables ESR bits 6
*SRE 32 ‘enables StatusByte bit 5
*ESR? ‘reads ESR Register bits
E? ‘reads Modbus Error Register
3.4.4 Questionable Registers and Digital Inputs
The Questionable Registers lets the user read bits that report CRC errors,
Exception message types or a timeout (no response message received). Bit
alignments are shown in Figure 3-1. The Questionable Transition Register
filters the inputs and passes only the enabled state changes to the Question-
able Event Register. The Questionable Event Register bits becomes true
(1) when the positive transition bit is enabled and the associated condition
register bit makes a 0 to 1 transition. When both transitions are selected
for the same bit, the corresponding Questionable Event Register bit sets
whenever the digital input changes state. The Questionable Event Register
is cleared when it is read.
The Questionable Registers are queried with the SCPI STATUS branch
commands.
The 4899A can be set to monitor the bits in the Questionable Register and
generate a SRQ when they change state. The following example sets the
Questionable Event register to monitor the CRC and Timeout bits by cap-
turing a positive transition on bits 12 and 13. The decimal value for bit 12
is 4096 and the decimal value for bit 13 is 8192.
STAT:QUES:PTR 12298 ‘enables bits 12 and 13 to set
on a positive transition
Because summing large decimal values is confusing, it is better to use HEX
values that are easier to write. i.e.
STAT:QUES:PTR #h3000 ‘same as 12298 decimal