MC68000 MOTOROLA [Motorola, Inc], MC68000 Datasheet - Page 171

• Manufacturer Part Number: MC68000
• Manufacturer: MOTOROLA [Motorola, Inc]

4.5.11.7 UART Control Characters and Flow Control
The UART has the capability 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 char-
acters 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 gen-
erated. 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.
The UART uses a table of 16-bit entries to support control-character recognition. 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 4-19.
RCCR—Received Control Character Register
CHARACTER7–CHARACTER1—Control Character Value
MOTOROLA
OFFSET + 0
OFFSET + 2
OFFSET + 4
OFFSET + 6
OFFSET +
Upon a control character match for which the reject bit is set, the UART will write the con-
trol character into the RCCR and generate a maskable interrupt. The M68000 core must
process the interrupt and read the RCCR before a second control character arrives. Fail-
ure to do so will result in the UART overwriting the first control character.
These fields define control characters that should be compared to the incoming character.
For 7-bit characters, the eighth bit (bit 7) should be zero.
10
15
E
E
E
E
To disable all functions of the control characters and flow control
table, initialize CHARACTER1 to $8000 and CHARACTER8 to
$0000.
14
R
R
R
R
REA
13
Figure 4-19. UART Control Characters Table
12
I
CT
11
MC68302 USER’S MANUAL
10
0
NOTE
9
0
A
8
•
•
•
7
Communications Processor (CP)
CHARACTER1
CHARACTER2
CHARACTER3
CHARACTER8
RCCR
4-51
0