Datasheet

Chapter 13 Serial Communications Interface (S08SCIV4)
MC9S08DN60 Series Data Sheet, Rev 3
238 Freescale Semiconductor
Table 13-5. SCI1S1 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
SCI1S1 with TDRE = 1 and then write to the SCI data register (SCI1D).
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 SCI1S1 with TC = 1 and then doing one of the following three things:
• Write to the SCI data register (SCI1D) to transmit new data
• Queue a preamble by changing TE from 0 to 1
• Queue a break character by writing 1 to SBK in SCI1C2
5
RDRF
Receive Data Register Full Flag — RDRF becomes set when a character transfers from the receive shifter into
the receive data register (SCI1D). To clear RDRF, read SCI1S1 with RDRF = 1 and then read the SCI data
register (SCI1D).
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 SCI1S1 with IDLE = 1 and then read the SCI data register (SCI1D). 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 SCI1D yet. In this case, the new
character (and all associated error information) is lost because there is no room to move it into SCI1D. To clear
OR, read SCI1S1 with OR = 1 and then read the SCI data register (SCI1D).
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 SCI1S1 and then read the SCI data register (SCI1D).
0 No noise detected.
1 Noise detected in the received character in SCI1D.