8 communications commands, Section 5.8 on – INFICON STM-2XM 2-Channel Rate/Thickness Monitor User Manual
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STM-2XM Operating Manual
5.8 Communications Commands
STM-2XM uses command prefix 0x80 to introduce command sequences. The data
payload that follows 0x80 are standard ASCII character sequences. This
vocabulary is documented in
section 5.5.2.1, Command Format, on page 5-6
.
Common commands have the same initial character sequences, and are
distinguished by variable numeric arguments which further specify the intended
action or target of the command/query.
Therefore, only the data payload content which distinguishes these commands are
found in this section.
All responses conform to the SMDP specification (refer to
) with the lower four bits of the returned <CMD_RSP> byte being a non-zero
value in the range of 1 to 15. The upper 4 bits are the same as the host command
group (CmdOpcode_xxx), 3 to 8. The lower three bits have the value 1 to 7 as
defined in
section 5.5.2.1.3 on page 5-11
. This value indicates whether the receiver
could process the query or found fault with it. If the address is not matched with a
slave, the checksum of the frame fails, or the command is otherwise improper, no
response is returned by the slave.
The fourth bit (D3, 8 weight) is a power fail flag bit, and the slave replies with this
bit set when the platform has been reset, until such a time as the master sends one
of the following:
Acknowledge-power-fail command (CmdOpcode_ACKPF 0x60), low level
SMDP message
USRAPI_ackPfail (?) command, application specific command (0x80)
The message from the master clears the power fail flag such that the status bit, D3,
of all subsequent replies is now zero. This allows the master to detect at the earliest
transaction (first valid communications after reboot/reset) that the slave device has
been reset and needs to be re-synchronized. This might be considered a fatal error
(power supply was reset and system state harmed), a soft error which can be
recovered from, or a non-issue requiring no intervention.