Crystal APM Advanced Pressure Module User Manual
Page 9
Communications
7
APM CPF Series Operation Manual
Command Processing
The data entered into the module is processed as follows:
•
Data is taken as 7-bit ASCII.
•
Characters are discarded if their decimal equivalent is less than 32 (space), except 10 (LF) and 13 (CR).
•
The most significant data bit is ignored.
•
Upper or lower case is acceptable.
•
More than one command (Compound Commands) may be entered on one line. Commands are separated by semi-colons. For example,
PRES_UNIT KPA;FAULT?
Response Data Types
The data returned by the module can be divided into four types:
X
Integer
For most computers and controllers, integers are decimal numbers ranging from
-32768
to
32768
. For example,
FAULT?
could return an integer of
117
. Refer
to the
for more information on error codes.
X
Floating
Floating numbers have up to 5 significant figures and exponents. For example,
VAL?
might return
25.345
PSI
.
X
Character Response Data (CRD)
Character Response Data is data returned as keywords. For example,
PRES_UNIT?
might return
PSI
.
X
Indefinite ASCII (IAD)
Indefinite ASCII are any characters followed by a terminator. For example,
*IDN
might return
CRYSTAL, APM003C, 678123, R130000.31/R08009.13
.
Module Status
X
Error Queue
If an error occurs due to invalid input or buffer overflow, its error code is sent to a 15 entry error queue. An error code is read from the queue with the
FAULT?
command. When the error queue is empty,
FAULT?
returns
0
. The error queue is cleared when power is reset or when the clear command
*CLS
is entered.
X
Input Buffer
The module stores all received data in a 128 character input buffer, which accommodates varying character input speeds.. If the input command/symbol
stream is too fast, the module will send the
XOFF
command when the input buffer is full. When the module is able to continue to receive commands, it will
generate the
XON
command. The module can receive up to eight more characters after the
XOFF
command has been sent. If more characters are received, it
will stop receiving, clear the input buffers, interrupt command execution, and flag the error
120
(Input Buffer overflow).