Manual

53ML5100A Manual Loading Station
Supplement to the Instruction Bulletin
8 Datalink Communications
4.1 Protocol
The Datalink protocol requires the host personal computer to initiate all transactions. There are two basic
categories for all of the Datalink message types: Interrogate, which is used to read data from an
addressed instrument, and Change, which is used to alter a value in an addressed instrument. The
addressed instrument decodes the message and provides an appropriate response. The protocol defini-
tions for the Datalink message types are provided in Table 4-1.
Table 4-1. Message Field Definitions
Symbol Title Definition
SOH Start of Header This character, 7E, denotes the beginning of a message.
CMD Command 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: Interrogate, Change, Change Bits,
Acknowledge, Response. The commands are covered in Section
4.1.1, Message Types.
I.A. Controller Address The address of the instrument responding to the transaction. It must
be within a range of 00-1F (00-31 decimal).
NUM Number The number of data bytes transferred or requested. The NUM must
be in a range of 00-32 decimal.
LO-ADD Lower Address Bits The least significant 8 bits of a 16 bit instrument address.
HI-ADD Higher Address Bits The most significant 8 bits of a 16 bit instrument address.
DATA An 8 bit data byte.
XXXX Represents a variable number of data bytes.
MASK An 8 bit byte where each bit, called a flag, is dedicated to an event
that is permitted or prohibited, depending on the flag setting.
If the flag is set to 0, the event is permitted.
If the flag is set to 1, the event is prohibited.
STATE Represents the bit settings of a particular byte: which bits are set
to 1, and which bits are set to 0.
LRC Longitudinal
Redundancy
Character
Is a character written at the end of the message that represents the
byte content of the message and is checked to ensure data was not
lost in transmission. It is the sum of all bytes Modulo 256 of the
message not including the SOH character or its own bit settings
(LRC).