HCS08 datasheet(208/316 Pages) NXP

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Serial Communications Interface (S08SCIV4)

MC9S08SG8 MCU Series Data Sheet, Rev. 8

208

Freescale Semiconductor

Table 14-5. SCIS1 Field Descriptions

Field

Description

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.

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

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.

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.

Receiver Overrun Flag — OR is set when a new serial character is ready to be transferred to the receive data

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).

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.

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