5702269-C I/O Communication and Control 4-55
Pinnacle™ Plus+ 10 kW
addresses. Address 0 (zero) is reserved for the AE Bus broadcast address; when this
address is used in a host-originated packet, all units execute the packet (but do not
respond back to the host).
The remaining three bits tell the receiving unit how long the Data field is so that the
unit can determine when the entire message has been received.
Note: The value in these bits should refer only to the number of actual data bytes. Do
not include the checksum byte when calculating the value for these bits.
The Header field (address and length) must be at the beginning of the message packet
so that the receiving unit can compute the length of the packet after receiving the first
byte.
COMMAND
This field contains a one-byte value: 00h to FFh (0 to 255). If the message packet
originates with the host computer, this value specifies the purpose of the message
packet. If the message originates with the Pinnacle Plus+ unit, the value specifies the
command to which it is responding. See “AE Bus Commands” on page 4-59 for a
complete list of AE Bus commands.
OPTIONAL LENGTH BYTE
This field supplements the Header field and exists only when the length bits in the
Header field contain a value of 7. Under those circumstances, the Optional field
contains a value only when the length bits in the Header field contain a value of 7. (A
value of 7 indicates that the Data field contains more than 6 bytes of data.) Under
those circumstances, the Optional field contains a one-byte value (between 0 and 255)
indicating the number of data bytes.
DATA (DATA BYTES)
The Data field can contain from 0 to 255 bytes of binary data, which are interpreted in
various ways, depending on the value that appears in the Command field. The Data
field typically contains data or a CSR (see “Creating an Ideal AE Bus
Communications Transaction” on page -56), depending on what was requested. Since
some commands do not require data, sometimes the Data field is not present.
If the value specified in the length bits of the Header field is 0 to 6, the Pinnacle Plus+
unit expects 0 to 6 bytes of data. However, if the value in the Header field is 7, the
Pinnacle Plus+ unit looks for an additional eight-bit byte after the Command field (the
Optional field) and uses this value for the data byte count.
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