MC68CK338
MC68CK338TS/D
MOTOROLA
77
NF — Noise Error Flag
0 = No noise detected on the received data
1 = Noise occurred on the received data
NF is set when the SCI receiver detects noise on a valid start bit, on any data bit, or on a stop bit. It is
not set by noise on the idle line or on invalid start bits. Each bit is sampled three times. If none of the
three samples are the same logic level, the majority value is used for the received data value, and NF
is set. NF is not set until an entire frame is received and RDRF is set.
FE — Framing Error Flag
0 = No framing error on the received data.
1 = Framing error or break occurred on the received data.
FE is set when the SCI receiver detects a zero where a stop bit was to have occurred. FE is not set until
the entire frame is received and RDRF is set. A break can also cause FE to be set. It is possible to miss
a framing error if RXD happens to be at logic level one at the time the stop bit is expected.
PF — Parity Error Flag
0 = No parity error on the received data
1 = Parity error occurred on the received data
PF is set when the SCI receiver detects a parity error. PF is not set until the entire frame is received and
RDRF is set.
SCDR contains two data registers at the same address. The receive data register is a read-only register
that contains data received by the SCI. The data comes into the receive serial shifter and is transferred
to the receive data register. The transmit data register is a write-only register that contains data to be
transmitted. The data is first written to the transmit data register, then transferred to the transmit serial
shifter, where additional format bits are added before transmission. R[7:0]/T[7:0] contain either the first
eight data bits received when SCDR is read, or the first eight data bits to be transmitted when SCDR is
written. R8/T8 are used when the SCI is configured for 9-bit operation. When it is configured for 8-bit
operation, they have no meaning or effect.
SCDR —
SCI Data Register
$YFFC0E
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
R8/T8
R7/T7
R6/T6
R5/T5
R4/T4
R3/T3
R2/T2
R1/T1
R0/T0
RESET:
0
0
0
0
0
0
0
U
U
U
U
U
U
U
U
U