GE 90-30 PLC Series Installation And Hardware Manual page 124

Breakfree SNP Protocol
Breakfree SNP became the default protocol on all serial ports on the Series 90-30 CPUs, starting
with Firmware Release 9.00 for CPUs 350–364, and Firmware Release 8.20 for CPUs 311–341.
The breakfree feature makes the protocol compatible with a wider variety of modems. This feature
is compatible with existing SNP master units such as computers running PLC programming
software, or PCM modules. In a few applications, primarily where a combination of multi-drop
SNP communications and very short PLC sweep times are used, users may desire, for performance
reasons, to disable breakfree SNP. Breakfree SNP can be disabled and re-enabled via
Communications Request instructions. The Series 90 PLC Serial Communications User's Manual,
GFK-0582 documents these Communications Request instructions.
350–374 CPUs
The 350–374 group of CPUs was developed to meet the needs of customers requiring increased
memory size, faster processing speed, and additional features not available on the 311–341 CPUs.
Compatibility With Hand-Held Programmer (HHP) and Memory Card
GFK-0356Q Chapter 5 CPUs
Service Request would read the TOD clock, an ADD instruction would add the correction
value to it, and another Service Request would write the new value to the TOD clock. A
possible drawback to this method is that if you replace your CPU you will have to determine a
new correction factor. Also, this method is affected by temperature changes, so its success is
based on holding the CPU's ambient temperature stable.
If more accuracy is needed, the PLC could be interfaced to a third party solution such as a
radio link or Global Positioning System (GPS) satellite system.
The user program in CPUs 350—374 cannot be viewed or edited with the Series 90-30 Hand-
Held Programmer (IC693PRG300). You must use one of the GE programming
software packages to create or edit CPU 350—-374 user programs.
The Series 90 Memory Card (used on the Hand-Held Programmer) is not supported by CPUs
350—374.
The only operations supported by the HHP's PROGRAM mode are writing to and reading from
the CPU's flash memory.
Although the HHP's CONFIG mode can be used to perform basic configuration of these
CPUs, it cannot handle specialized parameters such as those pertaining to the embedded
Ethernet Interface in the CPU364/374.
The HHP can be used to change the Time-of-Day Clock unless the Mem Protect configuration
parameter is set to Enabled and the keylock switch is in the ON (Protect) position.
The HHP can be used to edit data values in %R registers.
The HHP can be used to invoke or clear overrides on CPUs 350—364
The CPU374 does not support the HHP.
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