Siemens SIMATIC TIWAY 1 Manual de usuario descargar pdf (Pagina 189)

USING THE BDLC PROTOCOL

UNILINK HOST

ADAPTER B–4

USER MANUAL

B.2.2 Address

Field

The address field is eight bits in length and specifies the address of the

UNILINK

Host Adapter

which is to receive the message. Up to 32 adapters may

be multidropped on the

same host network as discussed in Paragraph 3.2.3. The

address is a unique value ranging from 0 to 31 and is set on the adapter with

dipswitches as described in Paragraph 3.3.1.1. There is no global address that

causes

all the adapters in a multipoint circuit to respond.

B.2.3 Contr

ol Field

The

control field is an eight bit field containing the BDLC codes for commands

and responses that control transmission, reception, and error recovery of

messages

from the host computer to the UNILINK Host Adapter

able B–1 lists

the minimum command set supported by this protocol. These commands are

described

in more detail in Paragraph B.3.

Table B–1 BDLC Protocol Command Set

Host Computer

Command

Transmission

SNRM

DISC

UNILINK Host

Adapter

Response

Transmission

I or RR

or RNR

___________________ ___________________

B.2.4 Information

Field

The 290-byte information field is divided into three subfields; the two-byte

length subfield, the one-byte UNILINK Host Adapter command code subfield,

and

up to 287 command parameter data bytes.

The length subfield contains the

hexadecimal count of the number of bytes in the information field. The smallest

information field will contain the length subfield and the command code

subfield

for a minimum count of three or 0003. Inserted DLEs are not included

the length count. The exception to this format is given in the

discussion on the

FRMR

response in Paragraph B.5.7.

1 2 ... 184 185 186 187 188 189 190 191 192 193 194 ... 207 208

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