Uart Control Character Recognition - Motorola MC68302 User Manual

Each UART controller has two 8-bit address registers (UADDR1 and
UADDR2) for address recognition. In the automatic mode, the incoming
address is checked against the UART address registers. Upon an address
match, the address match (M) bit in the BD is set/cleared to indicate which
address character was matched. The data following it is written to the data
buffers.
NOTE
For 7-bit characters, the eighth bit in UADDR1 and UADDR2 should
be zero.
4.5.11.7 UART CONTROL CHARACTER RECOGNITION.
The UART has the capa-
bility to recognize special control characters. These characters may be used
when the UART functions in a message-oriented environment. Up to eight
control characters may be defined by the user in the control characters table.
Each of these characters may be either stored (written to the receive buffer,
after which the current buffer is closed and a new receive buffer taken) or
rejected. If rejected, the character is written to the received control character
register (RCCR) in internal RAM, and a maskable interrupt is generated. This
method is useful for notifying the user of the arrival of control characters
(e.g., XOFF) that are not part of the received messages.
OFFSET+ 0
OFFSET+ 2
OFFSET+ 4
OFFSET+ 6
The UART uses a table of 16-bit entries to support control-character recog-
nition. Each entry consists of the control character, an end-of-table bit, and
a reject character bit. The control characters table is shown in Figure 4-9.
RCCR - Received Control Character Register
Upon a control character match for which the reject bit is set, the UART
will write the control character into the RCCR and generate a maskable
15 14 13
RCCR
E R CHARACTER1
E R CHARACTER2
E R CHARACTER3
OFFSET
~E~'
_E _ _
R~'----------~------C-HA_RA_CT_ER_s
_ _ _ _ _
~
Figure 4-9. UART Control Characters Table
MOTOROLA MC68302 USER'S MANUAL
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