Serial Management Controllers (SMCs)
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Freescale Semiconductor
29-11
29.3.3
SMC UART Channel Transmission Process
The UART transmitter is designed to work with almost no intervention from the core. When the core
enables the SMC transmitter, it starts sending idles, which are defined as the full character length of logic
high. The SMC immediately polls the first BD in the transmit channel BD table and once every character
time after that, depending on character length. When there is a message to transmit, the SMC fetches data
from memory and starts sending the message.
When a BD data is completely written to the transmit FIFO, the SMC writes the message status bits into
the BD and clears R. An interrupt is issued if the I bit in the BD is set. If the next TxBD is ready, the data
from its buffer is appended to the previous data and sent over the transmit pin without any gaps between
buffers. If the next TxBD is not ready, the SMC starts sending idles and waits for the next TxBD to be
ready.
By appropriately setting the I bit in each BD, interrupts can be generated after each buffer, a specific buffer,
or each block is sent. The SMC then proceeds to the next BD. If the CM bit is set in the TxBD, the R bit
is not cleared, allowing a buffer to be automatically resent next time the CP accesses this buffer. For
instance, if a single TxBD is initialized with the CM and W bits set, the buffer is sent continuously until R
is cleared in the BD.
29.3.4
SMC UART Channel Reception Process
When the core enables the SMC receiver, it enters
HUNT
mode and waits for the first character. The CP
then checks the first RxBD to see if it is empty and starts storing characters in the buffer. When the buffer
is full or the MAX_IDL timer expires (if enabled), the SMC clears the E bit in the BD and generates an
interrupt if the I bit in the BD is set. If incoming data exceeds the buffer’s length, the SMC fetches the next
BD, and, if it is empty, continues transferring data to this BD’s buffer. If CM is set in the RxBD, the E bit
is not cleared, so the CP can overwrite this buffer on its next access.
0x2C
BRKLN
Hword Last received break length. Holds the length of the last received break character sequence
measured in character units. For example, if the receive signal is low for 20 bit times and the
defined character length is 10 bits, BRKLN = 0x002, indicating that the break sequence is at
least 2 characters long. BRKLN is accurate to within one character length.
0x2E
BRKEC
Hword Receive break condition counter. Counts break conditions on the line. A break condition may
last for hundreds of bit times, yet BRKEC increments only once during that period.
0x30
BRKCR
Hword Break count register (transmit). Determines the number of break characters the UART
controller sends when the SMC sends a break character sequence after a
STOP
TRANSMIT
command. For 8 data bits, no parity, 1 stop bit, and 1 start bit, each break character is 10
zeros.
0x32
R_MASK
Hword Temporary bit mask.
1
From SMC base address. SMC base = IMMR + 0x3E80 (SMC1), 0x3F80 (SMC2).
Table 29-4. SMC UART-Specific Parameter RAM Memory Map (continued)
Offset
1
Name
Width
Description
Содержание PowerQUICC MPC870
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