ProSoft Technology MVI69-GSC - Manual (Page 77)

MVI69-GSC ♦ CompactLogix or MicroLogix Platform Reference
Generic ASCII Serial Communication Module User Manual
ProSoft Technology, Inc. Page 77 of 102
September 24, 2010
Block Request from the Processor to the Module
These blocks of data are used to transfer information from the CompactLogix
processor to the module. The structure of the output image used to transfer this
data is shown below:
Word Offset Description
Port 1 0 Block Sequence Number (Read block number as sent by module) (0 to
127)
1 Inter-character delay for this message (milliseconds between
characters)
2 Number of characters to transmit on Port 1 (0 to 50)
3 to 27 Port 1 ASCII character codes to transmit (up to 50 ASCII characters)
Port 2 28 Inter-character delay for this message (milliseconds between
characters)
29 Number of characters to transmit on Port 2 (0 to 50)
30 to 54 Port 2 ASCII character codes to transmit (up to 50 ASCII characters)
55 to 59 Reserved
The Block Sequence Number is that received on the last read block transfer
through the input image on the module. The ladder logic should copy this value
from byte 0 of the input image to byte 0 of output image in the ladder logic. This
must be 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 byte 0 of the output image. If the number of characters to
transmit in the write block is not set to zero (non-zero value in bytes 2 and 29),
this indicates to the module there is data present in the block that needs to be
transmitted. If the selected port is not already busy transmitting data from a
previous write block, the data in the block will be moved to the port’s transmit
buffer and sent out the port as soon as possible.
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 in the write block
output image along with the length and set the inter-character delay byte (bytes 1
and 28) to a value of 200 in the module’s output image 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.