Table of Contents
Advertisement
ERROR asserted does not preclude more operations from occuring; more data packets can be
received or transmitted. The error line needs to be polled after each operation to determine the
condition of the SKB switch.
Commands
Architecture Overview
Instructions and queries are received by the SKB module as command packets. Command
packets describe a method of encapsulating a command opcode, a length code, and applicable
parameter data in a format that can be interpreted by the command processor of the instrument
module firmware.
Command packets are the only available means of moving data into and out of the SKB module.
External communication drivers and protocols are utilized to transmit and receive command
packets. For example, the parallel communication driver can directly transmit command packets,
while the serial communication driver can implement a protocol that embeds command packets
within larger protocol packets.
Command Packet Format
Essentially all communication with the SKB module, regardless of interface or protocol used, is
accomplished via command packets.
A standard command packet can be up to 256 bytes in length.
The first byte is always an opcode, which can be any number between 0 and 127. The most
significant bit (MSB) is never set in a command packet opcode.
The second byte is always the length, in bytes, of the following parameter data. The value of the
length byte corresponds to the number of bytes in the parameter data section of the command
packet, regardless of the actual data type represented by the binary parameter data.
The minimum length of a command packet is two bytes. The opcode and length (even if zero)
must be transmitted to the SKB module.
Command packets appear as follows:
OP
LEN
DATA
where OP = opcode and LEN = length.
The communication architecture of the SKB switch does not implement a command-response
scheme. Each command packet sent is not necessarily answered with a response packet. Only
those opcodes that represent a query generate a response packet.
Operating and Maintenance Instructions – 30
Advertisement
Table of Contents
