SCC UART Mode
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Freescale Semiconductor
22-13
22.16 UART Mode Register (PSMR)
For UART mode, the SCC protocol-specific mode register (PSMR) is called the UART mode register.
Many bits can be modified while the receiver and transmitter are enabled.
Figure 22-6
shows the PSMR
in UART mode.
Table 22-9
describes PSMR UART fields.
Framing
The UART reports a framing errors when it receives a character with no stop bit, regardless of the
mode. The channel writes the received character to the buffer, closes it, sets RxBD[FR], generates
the RX interrupt if not masked, increments FRMEC, but does not check parity for this character. In
automatic multidrop mode, the receiver immediately enters hunt mode. If the UART allows data with
no stop bits (PSMR[RZS] = 1) when in synchronous mode (PSMR[SYN] = 1), framing errors are
reported but reception continues assuming the unexpected zero is the start bit of the next character;
in this case, the user may ignore a reported framing error until multiple framing errors occur within
a short period.
Break Sequence When the first break sequence is received, the UART increments the break error counter BRKEC.
It updates BRKLN when the sequence completes. After the first 1 is received, the UART sets
SCCE[BRKE], which generates an interrupt if not masked. If the UART is receiving characters when
it receives a break, it closes the Rx buffer, sets RxBD[BR], and sets SCCE[RX], which can generate
an interrupt if not masked. If PSMR[RZS] = 1 when the UART is in synchronous mode, a break
sequence is detected after two successive break characters are received.
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Field FLC
SL
CL
UM
FRZ
RZS
SYN DRT
—
PEN
RPM
TPM
Reset
0
R/W
R/W
Addr
0xA28 (PSMR2), 0xA48 (PSMR3), 0xA68 (PSMR4)
Figure 22-6. Protocol-Specific Mode Register for UART (PSMR)
Table 22-9. PSMR UART Field Descriptions
Bit
Name
Description
0
FLC
Flow control
0 Normal operation. The GSMR and port C registers determine the mode of CTS.
1 Asynchronous flow control. When CTS is negated, the transmitter stops at the end of the current
character. If CTS is negated past the middle of the current character, the next full character is sent
before transmission stops. When CTS is asserted again, transmission continues where it left off
and no CTS lost error is reported. Only idle characters are sent while CTS is negated.
1
SL
Stop length. Selects the number of stop bits the SCC sends. SL can be modified on the fly. The
receiver is always enabled for one stop bit unless the SCC UART is in synchronous mode and
PSMR[RZS] is set. Fractional stop bits are configured in the DSR.
0 One stop bit
1 Two stop bits
Table 22-8. Reception Errors (continued)
Error
Description
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