Table of Contents
Advertisement
the preamble bit in a BD is set, the SCC will send a preamble sequence before
transmitting that data buffer.
4.5.11.10 WAKEUP TIMER.
By issuing the ENTER HUNT MODE command, the
user can temporarily disable the UART receiver. It will remain inactive until
an idle or address character is recognized (depending on the setting of ML TD).
If the UART is still in the process of receiving a message that the user has
already decided to discard, the message may be aborted by issuing the
ENTER HUNT MODE command. The UART receiver will be re-enabled when
the message is finished by detecting the idle line (if MLTD=O) or by the
address bit of the next message (if MLTD = 1 ).
When the receiver is in sleep mode and a break sequence is received, the
receiver will increment the BRKEC counter and generate the BRK interrupt -
(if enabled).
'
4.5.11.11 UART ERROR-HANDLING PROCEDURE.
The UART controller reports
character reception and transmission error conditions through the channel
BDs, the error counters, and the UART event register (SCCE). The modem
interface lines can also be monitored directly by the
sec
status register.
Transmission Error
Clear to Send Lost During Character Transmission. When this error occurs
and the channel is not programmed to control this line with software, the
channel terminates buffer transmission, closes the buffer, sets the CST lost
(CT) bit in the BD, and generates the TX interrupt (if enabled). The channel
will resume transmission after the reception of the RESTART TRANSMIT
command.
Reception Errors
1. Overrun Error. The UART controller maintains an internal two-byte FIFO
for receiving data. The CP begins programming the SDMA channel (if
the data buffer is in external memory) when the first byte is received
into the FIFO. When a receiver FIFO overrun occurs, the channel writes
the received character into the internal FIFO over the previously received
character (the previous character and its status bits are lost). Then the
channel writes the received character to the buffer, closes the buffer,
sets overrun (OV) in the BD, and generates the RX interrupt (if enabled).
MOTOROLA
MC68302 USER'S MANUAL
4-41
Advertisement
Table of Contents
