Micromod Micro-DCI: 53SL6000 Single Loop Controller - Manual (Page 125)

Table C-2. Datalink Protocol
Symbol Description
CMD Command
It is the operation to be performed or a
description of the message that follows
the Command-I.A. byte. The Command-
I.A. byte has two fields: the Command
field (3 bits) and the I.A. field (5 bits).
There are five commands as follows:
Interrogate, Change, Change Bits,
Acknowledge, and Response.
NUM Number
The number of data bytes transferred or
requested. The NUM must be a range of
00-32 decimal.
LO-ADD Lower Address Bits
The least significant 8 bits of a 16 bit
controller address.
HI-ADD Higher Address Bits
The most significant 8 bits of a 16 bit
controller address.
DATA An 8 bit data byte.
XXXX Represents a variable number of data
bytes.
MASK Has a 0 in every bit position that is
selected to be forced to 0.
STATE Has a 1 in every bit position that is
selected to be forced to 1.
LRC It is the sum of all bytes Modolo 256 of the
message not including the SOH character
or its own bit settings (LRC). It is written at
the end of the message to ensure data
was not lost in transmission.
C.3.1 Message Types
The types of messages that are sent from the host
to the controllers on the datalink are formatted as
follows:
Host to Controller:
1. Interrogate - This message requests up to 20
H
consecutively stored bytes, beginning at the
specified memory address location of the ad-
dressed controller.
01111110 E0
H
+ I.A. NUM LO ADD HI ADD LRC
2. Change - This message sends up to 20
H
bytes
of new data to the addressed controller.
01111110 A0
H
+ I.A. NUM LO ADD HI ADD
Data 1 XXXXXXXXX Data N LRC
3. Change Bits - This message alters only the
specified bits in the specified bytes in the ad-
dressed controller. (NUM = 2N.)
01111110 CO
H
+ I.A. NUM LO ADD HI ADD
Mask 1 State 1 XXXX Mask N State N LRC
4. Acknowledge - This message signals the ad-
dressed controller that its last echoed change
message was received correctly; the controller
performs the change requested.
01111110 80
H
+ I.A.
Controller to Host:
1. Response - This message furnishes the data
requested by the Interrogate command of the
host. It is also used to echoe back the pre-
vious Change message of the host.
01111110 20
H
+ I.A. NUM LO ADD HI ADD Data
1 XXXXX Data N LRC
C.3.2 Transaction Examples
Example A - The host requests 9 bytes of data
beginning at hexadecimal memory address 1000
H
from the controller at datalink address 03.
1. Host sends Interrogate message.
01111110 11100011 00001001 00000000
SOH Cmd + I.A. NUM LO ADD
00010000 11111100
HI ADD LRC
2. Controller sends response message.
01111110 00100011 00001001 00000000
SOH Cmd + I.A. NUM LO ADD
00010000 XXXXX XXXXX XXXXX YYYYYYYY
HI ADD Data 1 . . . . . . . Data 9 LRC
Example B - The host sends 2 bytes of new data,
to be loaded into the controller at datalink address
03 beginning at hexadecimal memory address
1000
H
.
1. Host sends Change message.
01111110 10100011 00000010 00000000
SOH Cmd + I.A. NUM LO ADD
00010000 00001000 00001100 11001001
HI ADD Data 1 Data 2 LRC
53SL6000 Instruction Manual Appendix C. Datalink Protocol
C-2