Motorola MPC8260 - Manual (Page 709)

MOTOROLA Chapter 26. Serial Management Controllers (SMCs) 26-13
Part IV. Communications Processor Module
Table 26-5 describes receive commands issued to the CPCR.
26.3.6 Sending a Break
A break is an all-zeros character without stop bits. It is sent by issuing a STOP TRANSMIT
command. After sending any outstanding data, the SMC sends a character of consecutive
zeros, the number of which is the sum of the character length, plus the number of start,
parity, and stop bits. The SMC sends a programmable number of break characters
according to BRKCR and then reverts to idle or sends data if a
RESTART TRANSMIT is issued
before completion. When the break completes, the transmitter sends at least one idle
character before sending any data to guarantee recognition of a valid start bit.
26.3.7 Sending a Preamble
A preamble sequence provides a way to ensure that the line is idle before a new message
transfer begins. The length of the preamble sequence is constructed of consecutive ones that
are one-character long. If the preamble bit in a BD is set, the SMC sends a preamble
sequence before sending that buffer. For 8 data bits, no parity, 1 stop bit, and 1 start bit, a
preamble of 10 ones would be sent before the Þrst character in the buffer. If no preamble
sequence is sent, data from two ready transmit buffers can be sent on the transmit signal
with no delay between them.
26.3.8 Handling Errors in the SMC UART Controller
The SMC UART controller reports character reception error conditions via the channel
BDs and the SMCE. The SMC UART controller has no transmission errors.
Table 26-5. Receive Commands
Command Description
ENTER HUNT MODE Use the CLOSE RXBD command instead ENTER HUNT MODE for an SMC UART channel.
CLOSE RXBD Forces the SMC to close the current receive BD if it is currently being used and to use the next BD
in the list for any subsequently received data. If the SMC is not receiving data, no action is taken.
INIT RX
PARAMETERS
Initializes receive parameters in this serial channel parameter RAM to reset state. Issue it only if
the receiver is disabled.
INIT TX AND RX PARAMETERS resets both receive and transmit parameters.
Table 26-6. SMC UART Errors
Error Description
Overrun The SMC maintains a two-character length FIFO for receiving data. Data is moved to the buffer after the
Þrst character is received into the FIFO; if a receiver FIFO overrun occurs, the channel writes the
received character into the internal FIFO. It then writes the character to the buffer, closes it, sets the OV
bit in the BD, and generates the RXB interrupt if it is enabled. Reception then resumes as normal.
Overrun errors that occasionally occur when the line is idle can be ignored.
Parity The channel writes the received character to the buffer, closes it, sets the PR bit in the BD, and
generates the RXB interrupt if it is enabled. Reception then resumes as normal.
Idle
Sequence
Receive An idle is found when a character of all ones is received, at which point the channel counts consecutive
idle characters. If the count reaches MAX_IDL, the buffer is closed and an RXB interrupt is generated. If
no receive buffer is open, this does not generate an interrupt or any status information. The idle counter
is reset each time a character is received.