Using the Driver
9.3.2
Automatic Preamble/ID Sending and Message Queuing
Using the Echo_SendMessage()service, it is possible to queue messages for transmission. To queue
messages, you must specify the number of Preamble/ID sequences to preface the message with and, of
course, the spacing between each sequence. This information is stored in the transmit buffer (see
Section 9.5, “Buffer Formats”). To simplify timing, the spacing between messages is measured in bit
times. With this information stored alongside the message, a complete telegram can be sent without the
intervention of the application software.
When queueing messages with Echo_SendMessage(), the sequence of events is shown in Figure 9
Start
No
Tx Buf
Empty?
Yes
Application must clear the full flag.
Echo_SendMessage()will set the full
flag to indicate the Tx buffer is busy.
Fill Tx
Buffer
Invoke
Echo_ChangeBank()
if requirement
Invoke
Echo_SendMessage()
The Echo driver initiates the sending.
When possible, the message is copied
into the internal buffer, transmission
begins and the buffer full flag is cleared
to allow another message to be queued.
Yes
Another
message?
No
End
Figure 9. Querying Complete Telegrams
Software Drivers for MC33696, Rev. 1
Freescale Semiconductor
15
FREESCALE [ Freescale ]
