
Serial Communications Interface (SCI)
SCI Registers
MC68HC711D3 — Rev. 2
Data Sheet
MOTOROLA
Serial Communications Interface (SCI)
81
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 Bit
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 = Zero detected
6.7.5 Baud Rate Register
The baud rate register (BAUD) is used to select different baud rates for the SCI
system. The SCP1 and SCP0 bits function as a prescaler for the SCR2–SCR0 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 and can be changed at any time.
TCLR — Clear Baud Rate Counters (Test)
RCKB — SCI Baud Rate Clock Check (Test)
SCP1 and SCP0 — SCI Baud Rate Prescaler Select Bits
These two bits select a prescale factor for the SCI baud rate generator that
determines the highest possible baud rate.
Address:
$002B
Bit 7
654321
Bit 0
Read:
TCLR
0
SCP1
SCP0
RCKB
SCR2
SCR1
SCR0
Write:
Reset:
00000
U
U = Unaffected
Figure 6-7. Baud Rate Register (BAUD)
Table 6-1. Baud Rate Prescale Selects
SCP1
and SCP0
Divide
Internal Clock
By
Crystal Frequency in MHz
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