Datasheet

Functional Description
MC68HC908KX8 • MC68HC908KX2 • MC68HC08KX8 Data Sheet, Rev. 2.1
Freescale Semiconductor 115
12.4.2 Transmitter
Figure 12-5 shows the structure of the SCI transmitter.
12.4.2.1 Character Length
The transmitter can accommodate either 8-bit or 9-bit data. The state of the M bit in SCI control register 1
(SCC1) determines character length. When transmitting 9-bit data, bit T8 in SCI control register 3 (SCC3)
is the ninth bit (bit 8).
12.4.2.2 Character Transmission
During an SCI transmission, the transmit shift register shifts a character out to the TxD pin. The SCI data
register (SCDR) is the write-only buffer between the internal data bus and the transmit shift register. To
initiate an SCI transmission:
1. Enable the SCI by writing a 1 to the enable SCI bit (ENSCI) in SCI control register 1 (SCC1).
2. Enable the transmitter by writing a 1 to the transmitter enable bit (TE) in SCI control register 2
(SCC2).
3. Clear the SCI transmitter empty bit by first reading SCI status register 1 (SCS1) and then writing
to the SCDR.
4. Repeat step 3 for each subsequent transmission.
Addr.Register Name Bit 7654321Bit 0
$0013
SCI Control Register 1
(SCC1)
See page 125.
Read:
LOOPS ENSCI TXINV M WAKE ILTY PEN PTY
Write:
Reset:00000000
$0014
SCI Control Register 2
(SCC2)
See page 127.
Read:
SCTIE TCIE SCRIE ILIE TE RE RWU SBK
Write:
Reset:00000000
$0015
SCI Control Register 3
(SCC3)
See page 129.
Read: R8
T8 R R ORIE NEIE FEIE PEIE
Write:
Reset:UU000000
$0016
SCI Status Register 1
(SCS1)
See page 130.
Read: SCTE TC SCRF IDLE OR NF FE PE
Write:
Reset:11000000
$0017
SCI Status Register 2
(SCS2)
See page 132.
Read:000000BKFRPF
Write:
Reset:00000000
$0018
SCI Data Register
(SCDR)
See page 133.
Read: R7 R6 R5 R4 R3 R2 R1 R0
Write: T7 T6 T5 T4 T3 T2 T1 T0
Reset: Unaffected by reset
$0019
SCI Baud Rate Register
(SCBR)
See page 133.
Read: 0 0
SCP1 SCP0 R SCR2 SCR1 SCR0
Write:
Reset:00000000
= Unimplemented R = Reserved U = Unaffected
Figure 12-4. SCI I/O Register Summary