Hitachi H8S/2645, Hardware Manual

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13.2.7 Serial Status Register (SSR)
7
TDRE
1
R/(W)
*
6
RDRF
0
R/(W)
*
5
ORER
0
R/(W)
*
4
FER
0
R/(W)
*
3
PER
0
R/(W)
*
0
MPBT
0
R/W
2
TEND
1
R
1
MPB
0
R
Bit
Initial value
R/W
:
:
:
Note:
*
Only 0 can be written, to clear the flag.
SSR is an 8-bit register containing status flags that indicate the operating status of the SCI, and
multiprocessor bits.
SSR can be read or written to by the CPU at all times. However, 1 cannot be written to flags
TDRE, RDRF, ORER, PER, and FER. Also note that in order to clear these flags they must be
read as 1 beforehand. The TEND flag and MPB flag are read-only flags and cannot be modified.
SSR is initialized to H'84 by a reset, in standby mode, watch mode, subactive mode, and subsleep
mode or module stop mode.
Bit 7—Transmit Data Register Empty (TDRE): Indicates that data has been transferred from
TDR to TSR and the next serial data can be written to TDR.
Bit 7
TDRE Description
0 [Clearing conditions]
•
When 0 is written to TDRE after reading TDRE = 1
•
When the DTC is activated by a TXI interrupt and writes data to TDR
1 [Setting conditions] (Initial value)
•
When the TE bit in SCR is 0
•
When data is transferred from TDR to TSR and data can be written to TDR