ProSoft Technology MVI71-GSC - Manual (Page 56)

MVI71-GSC ♦ PLC Platform Reference
Generic Serial Communication Module
Page 56 of 82 ProSoft Technology, Inc.
January 31, 2008
The structure of the write file when the side-connect interface is utilized is shown
below:
Word Offset Description
0
Block Sequence Number (Read block number as set by module)(0 to
127)
1 Intercharacter delay for this message (milliseconds between
characters)
2 Number of characters to transmit on Port 1 (0 to 400)
Port 1
3 to 202 Port 1 data to transmit (400-byte data area)
203
Intercharacter delay for this message (milliseconds between
characters)
204 Number of characters to transmit on Port 2 (0 to 400)
Port 2
205 to 404 Port 2 data to transmit (400-byte data area)
405 to 499 Reserved
The Block Sequence Number is that received on the last read block transfer
through to the processor from the module. The ladder logic should copy this
value from word zero of the read block. This is the last operation performed when
constructing the write block. The module's program will trigger the process write
block function when a new value is recognized in word 0 of the write block. If the
number of characters to transmit in the write block is not set to zero, data to
transmit is present in the block. If the selected port is not busy transmitting data,
the data in the block will be moved to the port's transmit buffer and sent out the
port.
In order to pace the characters for the write operation, an inter-character delay
value is associated with each write message. For devices that do not buffer
received data, when interfacing with a modem in command mode or when
simulating keyboard or keypad entry, inter-character delays may be required. For
example, if the port is tied to a device that expects input with delays of 200
milliseconds between each character, place the data to send to the buffer along
with the length and set the inter-character word to a value of 200 in the
processor's ladder logic program. The message will be transmitted with a 200-
millisecond wait period between each character. Because this delay value is sent
from the processor for each write message, the inter-character delay can be set
independently for each message. For example, when writing AT commands to a
dial-up modem, an inter-character delay of 100 may be required. But when the
modem is in data mode, the inter-character delay can be set to 0. When the
delay is set to 0, the whole packet of data will be placed in the module's transmit
buffer at one time.