Emerson PNC001-A Series User Manual

PACSystems™ RX3i and RSTi-EP CPU Reference Manual Section 6
GFK-2222AK October 2019
Serial I/O, SNP & RTU Protocols 191
Therefore, it is important to be careful when disabling timeouts used by the SNP Slave
protocol.
When the CPU recognizes the programmer disconnect, it reinstalls RTU Slave protocol
unless a new protocol has been configured in the meantime. In that case, the CPU installs
the new protocol instead.
6.3.6.1 Example
1. COM1 is running RTU Slave protocol at 9600 baud.
2. A programmer is attached to COM1. The programmer is using 9600 baud.
3. The CPU installs SNP Slave on COM1 and the programmer communicates
normally.
4. The programmer stores a new configuration to COM1. The new configuration
sets the port for SNP Slave at 4800 baud (it will not take effect until the port loses
communications with the programmer).
5. When the CPU loses communications with the programmer, the new
configuration takes effect.
6.4 SNP Slave Protocol
PACSystems CPUs can communicate with Machine Edition software through either COM1
or COM2 using SNP slave protocol.
CPU COM1 is wired as an RS-232 Data Communications Equipment (DCE) port, and can
be connected directly using straight-through cable to one of the serial ports of a PC
running Machine Edition or other SNP master software.
CPU COM2 is wired for RS-485. If the SNP master does not have an RS-485 port, an RS-
485/RS-232 converter is required. The RX3i can use converter IC690ACC901, which uses
+5Vdc from the serial port. The CPU COM2 does not support IC690ACC901 and requires
an externally powered converter.
PACSystems provides the break free version of SNP, so that the SNP master does not need
to issue a break signal as part of the SNP attach sequence. However, the CPU responds
appropriately if a break signal is detected, by resetting the protocol to wait for another
attach sequence from the master.
PACSystems supports both point-to-point connections (single master/single slave) and
multi-drop connections (single master/multiple slaves).
For details on SNP protocol, refer to the Series 90 PLC Serial Communications User’s Manual,
GFK-0582.
CPE400 and CPL410 do not support this protocol.
6.4.1 Permanent Datagrams
Permanent datagrams survive after the SNP session that created them has been
terminated. This allows an SNP master device to periodically retrieve datagram data from
a number of different controllers on a multi-drop link, without the master having to
establish and write the datagram each time it reconnects to the controller.

Emerson PNC001-A Series Specifications

General

Brand	Emerson
Model	PNC001-A Series
Category	Controller
Language	English