SCC UART Mode
MPC885 PowerQUICC Family Reference Manual, Rev. 2
22-24
Freescale Semiconductor
For simplicity, assume that the line is not multidrop (no addresses are sent) and that each S-record fits into
a single buffer. Follow the basic UART initialization sequence above in
Section 22.21, “SCC UART
Programming Example,”
except allow for more and larger buffers and create the control character table as
described in
Table 22-14
.
To receive S-records, the core must wait for an RX interrupt, indicating that a complete S-record buffer
was received. Transmission requires assembling S-records into buffers and linking them to the TxBD
table; transmission can be paused when an XOFF character is received. This scheme minimizes the
number of interrupts the core receives (one per S-record) and relieves it from continually scanning for
control characters.
Table 22-14. UART Control Characters for S-Records Example
Character
Description
Line Feed
Both the E and R bits should be cleared. When an end-of-line character is received, the current buffer is
closed and made available to the core for processing. This buffer contains an entire S record that the
processor can now check and copy to memory or disk as required.
XOFF
E should be cleared; R should be set. Whenever the core receives a control-character-received (CCR)
interrupt and the RCCR contains XOFF, the software should immediately stop transmitting by setting
PSMR[FRZ]. This keeps the other station from losing data when it runs out of Rx buffers.
XON
XON should be received after XOFF. E should be cleared and R should be set. PSMR[FRZ] on the
transmitter should now be cleared. The CPM automatically resumes transmission of the serial line at the
point at which it was previously stopped. Like XOFF, the XON character is not stored in the receive buffer.
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