Rockwell Automation 1771-DA,D17716.5.13 U MNL 1771-DA ASCII I/O MODULE - Manual (Page 66)

Choosing Module Features
Chapter 3
3Ć24
Your ASCII module has a 1536 word (3072 byte) buffer for I/O data. The
percentage of buffer memory that you choose for input and output
depends on the operation of your ASCII device, and on relative
transmission rates into and out of the ASCII module’s I/O buffer. You
should proportion the size of your input and output buffers for maximum
storage (Table 2.K) so that the buffer does not fill and result in loss of
data, a condition known as spillover.
Table 2.K
I/O Buffer Size
When Your ASCII Device And When Select
Using
Code
Is bidirectional You want to divide buffer space equally 50% Input
50% Output
000
Can only generate input data to the ASCII module You want to maximize the number of characters that the
module's input buffer can store before spilling data
100% Input 001
Is bidrectional but most data is read from the ASCII
device
Same as block above 75% Input
25% Output
010
Is bidirectional but most data is written to your ASCII
device
You want to maximize the number of characters that the
module's output buffer can store before spilling data
25% Input
75% Output
011
Can only display data Same as block above 100% Output 100
Record the percentage of input to output that you want the buffer to have
by writing the corresponding 3-digit code in IW3(00-02). Use the form
(found at the end of this chapter) or the boxes below.
IW3
I/O
Buffer Size
02 01 00
Choosing I/O Buffer Size,
IW3(00Ć02)