mcf51ac256a Freescale Semiconductor, Inc, mcf51ac256a Datasheet - Page 416

• Manufacturer Part Number: mcf51ac256a
• Description: Mcf51ac Flexis
• Manufacturer: Freescale Semiconductor, Inc

Serial Communication Interface (SCI)Serial Communications Interface (SCIV4)
18-8
RDRF
TDRE
Field
IDLE
OR
TC
NF
7
6
5
4
3
2
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
SCIxS1 with TDRE set and then write to the SCI data register (SCIxD).
0 Transmit data register (buffer) full.
1 Transmit data register (buffer) empty.
Transmission Complete Flag. TC is set out of reset and when TDRE is set 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 SCIxS1 with TC set and then doing one of the following:
Receive Data Register Full Flag. RDRF becomes set when a character transfers from the receive shifter into the
receive data register (SCIxD). To clear RDRF, read SCIxS1 with RDRF set and then read the SCI data register
(SCIxD).
0 Receive data register empty.
1 Receive data register full.
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 is cleared, the receiver starts counting idle bit times after the start bit. 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 is set, the receiver doesn’t start
counting idle bit times until after the stop bit. 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 SCIxS1 with IDLE set and then read the SCI data register (SCIxD). After IDLE has been
cleared, it cannot become set again until after a new character has been received and RDRF has been set. IDLE
is set only once even if the receive line remains idle for an extended period.
0 No idle line detected.
1 Idle line was detected.
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 SCIxD yet. In this case, the new
character (and all associated error information) is lost because there is no room to move it into SCIxD. To clear
OR, read SCIxS1 with OR set and then read the SCI data register (SCIxD).
0 No overrun.
1 Receive overrun (new SCI data lost).
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 is set at the same time as RDRF is set for the character. To clear NF,
read SCIxS1 and then read the SCI data register (SCIxD).
0 No noise detected.
1 Noise detected in the received character in SCIxD.
• Write to the SCI data register (SCIxD) to transmit new data
• Queue a preamble by changing TE from 0 to 1
• Queue a break character by writing 1 to SBK in SCIxC2
MCF51AC256 ColdFire Integrated Microcontroller Reference Manual, Rev. 5
Table 18-5. SCIxS1 Field Descriptions
Description
Freescale Semiconductor