Motorola MPC8260 - Manual (Page 592)

20-8 MPC8260 PowerQUICC II UserÕs Manual MOTOROLA
Part IV. Communications Processor Module
Figure 20-2. Two UART Multidrop Configurations
20.9 Receiving Control Characters
The UART receiver can recognize special control characters used in a message-based
environment. Eight control characters can be deÞned in a control character table in the
UART parameter RAM. Each incoming character is compared to the table entries using a
mask (the received control character mask, RCCM) to strip donÕt cares. If a match occurs,
the received control character can either be written to the receive buffer or rejected.
If the received control character is not rejected, it is written to the receive buffer. The receive
buffer is then automatically closed to allow software to handle end-of-message characters.
Control characters that are not part of the actual message, such as XOFF, can be rejected.
Rejected characters bypass the receive buffer and are written directly to the received control
character register (RCCR), which triggers maskable interrupt.
The 16-bit entries in the control character table support control character recognition. Each
entry consists of the control character, a valid bit (end of table), and a reject bit. See
Figure 20-3.
Tx Rx
1
Tx Rx
2
Tx Rx
3
Tx Rx
4
Tx Rx Tx Rx Tx Rx Tx Rx
Slave 2 Slave 3 Slave 1 Master
UADDR1
UADDR2
PAODR
Choose wired-or operation in the port A
open-drain register to allow multiple transmit
pins to be directly connected
+ V
R
Two 8-bit addresses can be automatically
recognized in either configuration
+ V
R