MC68000 MOTOROLA [Motorola, Inc], MC68000 Datasheet - Page 172

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

Communications Processor (CP)
E—End of Table
R—Reject Character
Transmission of out-of-sequence characters is also supported and is normally used for the
transmission of flow control characters such as XON or XOFF. This is performed using the
last (eighth) entry in the UART control characters table. The UART will poll this character
whenever the transmitter is enabled for UART operation: during freeze, during buffer trans-
mission, and when no buffer is ready for transmission. The character is transmitted at a high-
er priority than the other characters in the transmit buffer (if any), but does not pre-empt
characters already in the transmit FIFO.
CHARACTER8—Control Character Value
The eighth entry in the UART control characters table is defined as follows:
E—Empty
R—Reject
REA—Ready
I—Interrupt
4-52
Must be one to use this entry as a flow control transmission character. To use this entry
instead as a receive control characters entry, this E bit (and all other E bits in the table)
should be zero.
Must be zero to use this entry as a flow control transmission character. For a receive con-
trol characters entry, it maintains its functionality as previously defined.
This bit is set by the M68000 core when the character is ready for transmission and will
remain one while the character is being transmitted. The CP clears this bit after transmis-
sion.
If set, the M68000 core will be interrupted when this character has been transmitted. (The
TX bit will be set in the UART event register.)
0 = This entry is valid. The lower eight bits will be checked against the incoming char-
1 = The entry is not valid. No valid entries lie beyond this entry.
0 = The character is not rejected but is written into the receive buffer. The buffer is then
1 = If this character is recognized, it will not be written to the receive buffer. Instead, it
acter.
closed, and a new receive buffer is used if there is more data in the message. A
maskable interrupt is generated in the RX bit of the UART event register.
is written to the RCCR, and a maskable interrupt is generated in the CCR bit in the
UART event register. The current buffer is not closed when a control character is
received with R set.
In tables with eight receive control characters, E is always zero.
MC68302 USER’S MANUAL
NOTE
MOTOROLA