
MOTOROLA
SERIAL COMMUNICATIONS INTERFACE
MC68HC11D3
7-8
TECHNICAL DATA
NF — Noise Error Flag
NF is set if majority sample logic detects anything other than a unanimous decision.
Clear NF by reading SCSR with NF set and then reading SCDR.
0 = Unanimous decision
1 = Noise detected
FE — Framing Error
FE is set when a 0 is detected where a stop bit was expected. Clear the FE flag by
reading SCSR with FE set and then reading SCDR.
0 = Stop bit detected
1 = 0 detected
7.6.5 Baud Rate Register (BAUD)
Use this register to select different baud rates for the SCI system. The SCP[1:0] bits
function as a prescaler for the SCR[2:0] bits. Together, these five bits provide multiple
baud rate combinations for a given crystal frequency. Normally, this register is written
once during initialization. The prescaler is set to its fastest rate by default out of reset,
rate selections.
TCLR — Clear Baud Rate Counters (Test)
RCKB — SCI Baud Rate Clock Check (Test)
SCP1, SCP0 — SCI Baud Rate Prescaler Selects
These two bits select a prescale factor for the SCI baud rate generator that determines
the highest possible baud rate.
SCR[2:0] — SCI Baud Rate Selects
These three bits select receiver and transmitter bit rate based on output from baud rate
prescaler stage.
BAUD — Baud Rate
$002B
Bit 7
654321
Bit 0
TCLR
0
SCP1
SCP0
RCKB
SCR2
SCR1
SCR0
RESET:
00000
U
Table 7-1 Baud Rate Prescale Selects
SCP[1:0]
Divide
Crystal Frequency in MHz
Internal Clock
By
4.0 MHz
(Baud)
8.0 MHz
(Baud)
10.0 MHz
(Baud)
12.0 MHz
(Baud)
0 0
1
62.50 K
125.0 K
156.25 K
187.5 K
0 1
3
20.83 K
41.67 K
52.08 K
62.5 K
1 0
4
15.625 K
31.25 K
38.4 K
46.88 K
1 1
13
4800
9600
12.02 K
14.42 K