Table 15-4. SCIxC2 Field Descriptions (continued)

 

 

 

Field

 

Description

 

 

2

Receiver Enable. When the SCI receiver is off, the RxD pin reverts to being a general-purpose port I/O pin. If

RE

LOOPS is set the RxD pin reverts to being a general-purpose I/O pin even if RE is set.

 

0

Receiver off.

 

1

Receiver on.

 

 

1

Receiver Wakeup Control. This bit can be written to 1 to place the SCI receiver in a standby state where it waits

RWU

for automatic hardware detection of a selected wakeup condition. The wakeup condition is 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 15.3.3.2, “Receiver Wakeup Operation,for more details.

 

0

Normal SCI receiver operation.

 

1

SCI receiver in standby waiting for wakeup condition.

 

 

0

Send Break. Writing a 1 and then a 0 to SBK queues a break character in the transmit data stream. Additional

SBK

break characters of 10 or 11 (13 or 14 if BRK13 = 1) bit times of logic 0 are queued as long as SBK is set.

 

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 15.3.2.1, “Send Break and

 

Queued Idle” for more details.

 

0

Normal transmitter operation.

 

1

Queue break character(s) to be sent.

 

 

 

15.2.4SCI Status Register 1 (SCIxS1)

This register has eight read-only status flags. Writes have no effect. Special software sequences (which do not involve writing to this register) clear these status flags.

R

W

Reset

7

6

5

4

3

2

1

0

TDRE

TC

RDRF

IDLE

OR

NF

FE

PF

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1

1

0

0

0

0

0

0

 

 

 

 

 

 

 

 

 

 

Figure 15-9. SCI Status Register 1 (SCIxS1)

 

 

 

Table 15-5. SCIxS1 Field Descriptions

 

 

 

 

 

Field

 

Description

 

 

 

7

Transmit Data Register Empty Flag. TDRE is set out of reset and when a transmit data value transfers from the

TDRE

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.

 

 

 

 

6

Transmission Complete Flag. TC is set out of reset and when TDRE is set and no data, preamble, or break

 

TC

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:

 

 

 

• 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

 

 

 

 

 

 

 

MCF51QE128 MCU Series Reference Manual, Rev. 3

 

 

 

 

Freescale Semiconductor

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Freescale Semiconductor MCF51QE128RM manual SCI Status Register 1 SCIxS1, Tdre Rdrf Idle