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Communications Capabilities
12.5.3 Assigning the Driver Number for a Communications Link
The number of the driver for the communications link is entered in system data word 46 (EA5C
thus activating the link.
Note
No other functions (e.g. PG/OP) are possible once the communications link has been
activated.
The operating system also enters an error code in system data word SD 46 if the specified driver is
not available or if coordination bytes have not been defined. Table 12-16 shows the contents of
system data word SD 46.
Byte
High-Order
Byte
Low-Order
Byte
*
Default value
12.5.4 Transmission
Control characters and useful data are transmitted over the interface in bit-serial mode.
When mode 2 is specified in system data word 55, a block check character (BCC) is transmitted at
the end of each frame. The BCC itself is protected by the specified parity, and is transferred at the
end of each frame. Mode 2 must be entered in system data word 55 to make this possible (see
Table 12-14).
Prior to transmission, the data is stored temporarily in a 1024-byte output buffer. An error is
flagged (see Table 12-19) if the output buffer does not have sufficient capacity to accommodate
the data to be transferred.
The receive data is entered temporarily in a 1024-byte input buffer before being forwarded to the
CPU's Receive mailbox via the application program.
12-42
Table 12-16. System Data Word SD 46
Contents
*
00
Same communications capabilities as the CPU 943
H
02
H
01
H
10
H
20
H
40
H
Description
Driver for communications link 3964 (R)
Error Codes
No driver for the communications link
No CBS
No CBR
No CBS and no CBR
S5-115U Manual
),
H
EWA 4NEB 811 6130-02b
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