Specifications

Sheet 8 of 39 Document 12245 Rev. I
If an ACK response is requested on every message, the host will know if a message was rejected (for any
reason) because it will not receive the quick ACK response.
1.8.3 ACK Responses
If requested, an ACK response will be generated as quickly as possible following receipt of the original
message. With a full duplex interface, if the unit is already transmitting when it becomes time to send an ACK
response, it will send the ACK as soon as it finishes transmitting the existing message. When using a half-
duplex interface, a delay of 1 byte time is introduced to allow time for the host to switch from transmitting to
receiving. The line must be idle during this time. Another delay of 1 byte time is always introduced when the
transmitter is turned on.
The timing of the ACK response (after the end of the host message) is as follows:
FULL DUPLEX interface:
MINIMUM: 1 BYTE TIME
MAXIMUM: (1 BYTE TIME + 1 ms), or as soon as the transmitter is done sending a message
HALF DUPLEX interface:
MINIMUM: 2 BYTE TIMES with idle line
MAXIMUM: (2 BYTE TIMES + 1 ms) with idle line
NOTE: If the half duplex line is not idle, the unit simply waits for the line to be idle for 1 BYTE TIME,
then generates the ACK response.
1.8.4 Replies
If a message generates a reply, that reply should start no more than 100 ms after the original host message.
With a full duplex interface, if the unit is already transmitting when it becomes time to send a reply, it will send
it as soon as the transmitter is finished. If a message generates both a reply and an ACK response, the ACK
response will always be first (according to ACK Response specifications), followed by the reply, within its
specified time frame.
The minimum time for a reply (with no ACK response) is the same as the minimum specification for an ACK
response above, depending on the interface.
2 Messages
Serial I/O messages are normally sent using the VertexRSI Serial I/O Message Framing Protocol. This
protocol imposes the following restrictions on the message content.
 The message data must contain at least one byte, and at most 249 bytes.
 The first byte is limited to a six-bit value ranging from 00 to 3E, excluding the values 02 and 03.
 No byte in the message data can be 02 or 03.
. . .

FRAMING HEADER
Instruction
Code (6 bits)
Message body
(optional)
. . .

FRAMING FOOTER
End Body
2A
MESSAGE DATA

Sub-Instruction
(optional
)
Data Value(s)
(optional)
In this protocol, the first byte of the message data is referred to as the instruction code, which ranges in value
from 00 to 20. Normally if there is a reply, it will contain the same instruction code as the host message.