SATEC SLC500 - Manual (Page 7)

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3 GENERAL OPERATION
3.1 Interfacing to the BASIC Module
The BASIC module interfaces with the SLC processor via the SLC backplane interface. Data
is transferred through SLC CPU Module M0 and M1 files as 16-bit signed integers up to
32767.
The data to be sent to the BASIC module must be placed in the M0 file. The size,
configuration, and contents of the M0 file are discussed in Section 4.2.
The data to be sent to the CPU is placed into the M1 file. There are three user-selectable
formats of data exchange. The structure and contents of these data sets are provided in
Appendix A and discussed in Section 4.1.
To guarantee data integrity during data transfer between the BASIC module and the CPU, a
special handshaking technique is applied. For handshaking implementation, two bits within one
word in the input image table and within one word in the output image table are used. These
are discussed in Section 4.3.
3.2 Principles of Operation
On power-up, the driver automatically enters a polling loop and continuously polls all the
Powermeters listed in the polling list. The driver checks the response time, message integrity
and data value ranges.
If the Powermeter response is OK, then data is placed to the CPU M1 file and the request to
the CPU for data reading is issued. After the CPU has read data from the M1 file, the driver
goes to the next Powermeter.
When the driver fails to receive an acceptable response from a certain Powermeter, it retries
twice. If the driver has failed to get any response from the Powermeter, then it considers the
Powermeter "dead" and disables it. The CPU is informed of the error by a non-zero error
code in word 64 of the M1 file. For the possible error codes, refer to Table 4.1.
Note that disabled Powermeters are resuscitated after 3-6 minutes depending on the number
of instruments being polled. On reconnecting a Powermeter, it goes back to the polling mode.
Before polling any Powermeter, the driver always checks whether there are any writes
pending in the CPU M0 file. If so, then the appropriate command is sent to the addressed
Powermeter or Powermeters, and driver goes back to the polling loop.