mc9s12e256 Freescale Semiconductor, Inc, mc9s12e256 Datasheet - Page 252

• Manufacturer Part Number: mc9s12e256
• Description: Hcs12 Microcontrollers 16-bit Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Chapter 8 Serial Communication Interface (SCIV4)
8.3.2.4
The SCISR1 and SCISR2 registers provide inputs to the MCU for generation of SCI interrupts. Also, these
registers can be polled by the MCU to check the status of these bits. The flag-clearing procedures require
that the status register be read followed by a read or write to the SCI data register. It is permissible to
execute other instructions between the two steps as long as it does not compromise the handling of I/O.
Note that the order of operations is important for flag clearing.
Read: anytime
Write: has no meaning or effect
252
Reset
RDRF
TDRE
Field
IDLE
TC
7
6
5
4
W
R
TDRE
Transmit Data Register Empty Flag — TDRE is set when the transmit shift register receives a byte from the
SCI data register. When TDRE is 1, the transmit data register (SCIDRH/L) is empty and can receive a new value
to transmit.Clear TDRE by reading SCI status register 1 (SCISR1), with TDRE set and then writing to SCI data
register low (SCIDRL).
0 No byte transferred to transmit shift register
1 Byte transferred to transmit shift register; transmit data register empty
Transmit Complete Flag — TC is set low when there is a transmission in progress or when a preamble or break
character is loaded. TC is set high when the TDRE flag is set and no data, preamble, or break character is being
transmitted.When TC is set, the TXD pin becomes idle (logic 1). Clear TC by reading SCI status register 1
(SCISR1) with TC set and then writing to SCI data register low (SCIDRL). TC is cleared automatically when data,
preamble, or break is queued and ready to be sent. TC is cleared in the event of a simultaneous set and clear of
the TC flag (transmission not complete).
0 Transmission in progress
1 No transmission in progress
Receive Data Register Full Flag — RDRF is set when the data in the receive shift register transfers to the SCI
data register. Clear RDRF by reading SCI status register 1 (SCISR1) with RDRF set and then reading SCI data
register low (SCIDRL).
0 Data not available in SCI data register
1 Received data available in SCI data register
Idle Line Flag
on the receiver input. After the IDLE flag is cleared, a valid frame must again set the RDRF flag before an idle
condition can set the IDLE flag.Clear IDLE by reading SCI status register 1 (SCISR1) with IDLE set and then
reading SCI data register low (SCIDRL).
0 Receiver input is either active now or has never become active since the IDLE flag was last cleared
1 Receiver input has become idle
SCI Status Register 1 (SCISR1)
1
7
= Unimplemented or Reserved
1
TC
— IDLE is set when 10 consecutive logic 1s (if M = 0) or 11 consecutive logic 1s (if M = 1) appear
1
6
Figure 8-7. SCI Status Register 1 (SCISR1)
Table 8-7. SCISR1 Field Descriptions
RDRF
MC9S12E256 Data Sheet, Rev. 1.08
0
5
IDLE
0
4
Description
OR
3
0
NF
0
2
Freescale Semiconductor
FE
0
1
PF
0
0