SCC UART Mode
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Freescale Semiconductor
22-5
22.5
Data-Handling Methods: Character- or Message-Based
An SCC UART controller uses the same BD table and buffer structures as the other protocols and supports
both multibuffer, message-based and single-buffer, character-based operation.
For character-based transfers, each character is sent with stop bits and parity and received into separate
1-byte buffers. A maskable interrupt is generated when each buffer is received.
In a message-based environment, transfers can be made on entire messages rather than on individual
characters. To simplify programming and save processor overhead, a message is transferred as a linked list
of buffers without core intervention. For example, before handling input data, a terminal driver may wait
for an end-of-line character or an idle timeout rather than be interrupted when each character is received.
Conversely, ASCII files can be sent as messages ending with an end-of-line character.
When receiving messages, up to eight control characters can be configured to mark the end of a message
or generate a maskable interrupt without being stored in the buffer. This option is useful when flow control
0x50
CHARACTER1
Hword
Control character 1–8. These characters define the Rx control characters on
which interrupts can be generated.
0x52
CHARACTER2
Hword
0x54
CHARACTER3
Hword
0x56
CHARACTER4
Hword
0x58
CHARACTER5
Hword
0x5A
CHARACTER6
Hword
0x5C
CHARACTER7
Hword
0x5E
CHARACTER8
Hword
0x60
RCCM
Hword
Receive control character mask. Used to mask comparison of
CHARACTER1–8 so classes of control characters can be defined. A one
enables the comparison, and a zero masks it.
0x62
RCCR
Hword
Receive control character register. Used to hold the last rejected control
character (not written to the Rx buffer). Generates a maskable interrupt. If the
core does not process the interrupt and read RCCR before a new control
character arrives, the previous control character is overwritten.
0x64
RLBC
Hword
Receive last break character. Used in synchronous UART when PSMR[RZS]
= 1; holds the last break character pattern. By counting zeros in RLBC, the
core can measure break length to a one-bit resolution. Read RLBC by
counting the zeros written from bit 0 to where the first one was written. RLBC
= 0b001xxxxxxxxxxxxx indicates two zeros; 0b1xxxxxxxxxxxxxxx indicates
no zeros.
Note that RLBC can be used in combination with BRKLN above to measure
the break length down to a bit resolution: (BRKLN + number of zeros in
RLBC).
1
From SCC base. SCC base = IMMR + 0x3D00 (SCC2) or 0x3E00 (SCC3) or 0x3F00 (SCC4)
Table 22-1. UART-Specific SCC Parameter RAM Memory Map (continued)
Offset
1
Name
Width
Description
Содержание PowerQUICC MPC870
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