
Functional Description and Application Information
Serial Communication Interface (S08SCIV4)
MM912F634
Freescale Semiconductor
115
4.15.2.4
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.
Table 132. SCI Status Register 1 (SCIS1)
Access: User read/write
76
543
210
R
TDRE
TC
RDRF
IDLE
OR
NF
FE
pF
W
Reset
1
100
00
Note:
103. Offset related to 0x0200 for blocking access and 0x300 for non blocking access within the global address space.
Table 133. SCIS1 Field Descriptions
Field
Description
7
TDRE
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.
6
TC
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
5
RDRF
Receive Data Register Full Flag — RDRF becomes set when a character transfers from the receive shifter into the receive
data register (SCID). To clear RDRF, read SCIS1 with RDRF = 1 and then read the SCI data register (SCID).
0 Receive data register empty.
1 Receive data register full.
4
IDLE
Idle Line Flag — IDLE is set when the SCI receive line becomes idle for a full character time after a period of activity. When
ILT = 0, the receiver starts counting idle bit times after the start bit. So if the receive character is all 1s, these bit times and the
stop bit time count toward the full character time of logic high (10 or 11 bit times depending on the M control bit) needed for the
receiver to detect an idle line. When ILT = 1, the receiver doesn’t start counting idle bit times until after the stop bit. So the stop
bit and any logic high bit times at the end of the previous character do not count toward the full character time of logic high
needed for the receiver to detect an idle line.
To clear IDLE, read SCIS1 with IDLE = 1 and then read the SCI data register (SCID). After IDLE has been cleared, it cannot
become set again until after a new character has been received and RDRF has been set. IDLE will get set only once even if
the receive line remains idle for an extended period.
0 No idle line detected.
1 Idle line was detected.
3
OR
Receiver Overrun Flag — OR is set when a new serial character is ready to be transferred to the receive data register (buffer),
but the previously received character has not been read from SCID yet. In this case, the new character (and all associated error
information) is lost because there is no room to move it into SCID. To clear OR, read SCIS1 with OR = 1 and then read the SCI
data register (SCID).
0 No overrun.
1 Receive overrun (new SCI data lost).
2
NF
Noise Flag — The advanced sampling technique used in the receiver takes seven samples during the start bit and three
samples in each data bit and the stop bit. If any of these samples disagrees with the rest of the samples within any bit time in
the frame, the flag NF will be set at the same time as the flag RDRF gets set for the character. To clear NF, read SCIS1 and
then read the SCI data register (SCID).
0 No noise detected.
1 Noise detected in the received character in SCID.