The protocol consists of 10 sequences, numbered 050 to 059 as follows:

Sequence Number	Description
050	DM area multiple word read
051	IR/SR area multiple word read
052	HR area multiple word read
053	LR area multiple word read
054	AR area multiple word read
055	DM area single word write
056	IR/SR area single word write
057	HR area single word write
058	LR area single word write
059	AR area single word write

Output & Input Words for All Read Sequences

Note: The output words are the middle operand of PMCR and are also known as source words and read words. The input words are the 3^rd operand of PMCR and are also known as destination words and write words.

Output Word	Description	Value
M	Size of table	0004
M+1	Unit number	0000-0031
M+2	Start address	0000-max address for memory area
M+3	Number of words to read	0001-0030
Input Word	Description	Value
N	Size of table	Returned by PMCR
N+1	End code	0000=OK, see Hostlink manual for error code descriptions
N+2 onwards	Data

Recommended Method to Perform A Read

• Clear word N & N+1 (i.e. set to zero)
• Set up the output words as described in the table above.
• Execute PMCR.
• When PMCR is complete check the value in word N & N+1. If word N remains at zero then there was no response from the slave PLC (i.e. timeout). If word N is 2 then the slave PLC returned an end code that will be stored in word N+1. If word N is greater than 2 and word N+1 is zero, the operation was successful.

Note 1: The data read from the slave PLC will be stored in reverse order in the master PLC.
Note 2: Never try to read more than 30 items in one message.

Read Operation Example

The master PLC wants to read 3 words of DM starting at DM0123 from slave unit 16. The first output word in the PMCR is set to DM0000. The first input word is set to DM0010.



Output & Input Words for All Write Sequences

Output Word	Description	Value
M	Size of table	0004
M+1	Unit number	0000-0031
M+2	Address	0000-max address for memory area
M+3	New value	0000-FFFF
Input Word	Description	Value
N	Size of table	Returned by PMCR
N+1	End code	0000=OK, see Hostlink manual for error code descriptions

Recommended Method to Perform A Write

• Clear word N & N+1 (i.e. set to zero)
• Set up the output words as described in the table above.
• Execute PMCR.
• When PMCR is complete check the value in word N & N+1. If word N remains at zero then there was no response from the slave PLC (i.e. timeout). If word N is 2 then the slave PLC responded. If N+1 is non-zero the write operation failed. If it is zero the write operation succeeded.

Write Operation Example

The master PLC wants to write a value of 1234 to DM0200 in slave unit 3. The first output word in the PMCR is set to DM0000. The first input word is set to DM0010.



Timeout & Retry Values

All the sequences have a one second timeout for sending the commands and another one second timeout for receiving the reply. If the sequence times out or an unexpected reply is received the sequence will automatically retry up to two times. After this the sequence will abort.
Attached are several protocol macros for HostLink.