MC9S08QG8_09 Datasheet, PDF (202/314 Pages) Freescale Semiconductor, Inc – HCS08 Microcontrollers

Serial Communications Interface (S08SCIV3)
Field
2
RE
1
RWU
0
SBK
Table 14-4. SCIC2 Register Field Descriptions (continued)
Description
Receiver Enable — When the SCI receiver is off, the RxD pin reverts to being a general-purpose port I/O pin. If
LOOPS = 1, the RxD pin reverts to being a general-purpose I/O pin even if RE = 1.
0 Receiver off.
1 Receiver on.
Receiver Wakeup Control — This bit can be written to 1 to place the SCI receiver in a standby state where it
waits for automatic hardware detection of a selected wakeup condition. The wakeup condition is either an idle
line between messages (WAKE = 0, idle-line wakeup), or a logic 1 in the most significant data bit in a character
(WAKE = 1, address-mark wakeup). Application software sets RWU and (normally) a selected hardware
condition automatically clears RWU. Refer to Section 14.3.3.2, “Receiver Wakeup Operation,” for more details.
0 Normal SCI receiver operation.
1 SCI receiver in standby waiting for wakeup condition.
Send Break — Writing a 1 and then a 0 to SBK queues a break character in the transmit data stream. Additional
break characters of 10 or 11 bit times of logic 0 are queued as long as SBK = 1. Depending on the timing of the
set and clear of SBK relative to the information currently being transmitted, a second break character may be
queued before software clears SBK. Refer to Section 14.3.2.1, “Send Break and Queued Idle,” for more details.
0 Normal transmitter operation.
1 Queue break character(s) to be sent.
14.2.4 SCI Status Register 1 (SCIS1)
This register has eight read-only status flags. Writes have no effect. Special software sequences (which do
not involve writing to this register) are used to clear these status flags.
7
6
5
4
3
2
1
0
R TDRE
TC
RDRF
IDLE
OR
NF
FE
PF
W
Reset
1
1
0
0
0
0
0
0
= Unimplemented or Reserved
Figure 14-9. SCI Status Register 1 (SCIS1)
Table 14-5. SCIS1 Register Field Descriptions
Field
7
TDRE
6
TC
Description
Transmit Data Register Empty Flag — TDRE is set out of reset and when a transmit data value transfers from
the transmit data buffer to the transmit shifter, leaving room for a new character in the buffer. To clear TDRE, read
SCIS1 with TDRE = 1 and then write to the SCI data register (SCID).
0 Transmit data register (buffer) full.
1 Transmit data register (buffer) empty.
Transmission Complete Flag — TC is set out of reset and when TDRE = 1 and no data, preamble, or break
character is being transmitted.
0 Transmitter active (sending data, a preamble, or a break).
1 Transmitter idle (transmission activity complete).
TC is cleared automatically by reading SCIS1 with TC = 1 and then doing one of the following three things:
• Write to the SCI data register (SCID) to transmit new data
• Queue a preamble by changing TE from 0 to 1
• Queue a break character by writing 1 to SBK in SCIC2
MC9S08QG8 and MC9S08QG4 Data Sheet, Rev. 5
200
Freescale Semiconductor