Renesas SH7041 Series, Hardware Manual, Page: 517 / 923

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14.2.7 Serial Status Register (SSR)
The serial status register (SSR) is an 8-bit register containing multiprocessor bit values, and status
flags that indicate SCI operating status.
The CPU can always read and write the SSR, but cannot write 1 in the status flags (TDRE, RDRF,
ORER, PER, and FER). These flags can be cleared to 0 only if they have first been read (after
being set to 1). Bits 2 (TEND) and 1 (MPB) are read-only bits that cannot be written. The SSR is
initialized to H'84 by a power-on reset or in standby mode. Manual reset does not initialize SSR.
Bit: 7 6 5 4 3 2 1 0
TDRE RDRF ORER FER PER TEND MPB MPBT
Initial value: 1 0 0 0 0 1 0 0
R/W: R/(W)
*
R/(W)
*
R/(W)
*
R/(W)
*
R/(W)
*
R R R/W
Note:
*
The only value that can be written is a 0 to clear the flag.
•
Bit 7—Transmit Data Register Empty (TDRE): Indicates that the SCI has loaded transmit data
from the TDR into the TSR and new serial transmit data can be written in the TDR.
Bit 7: TDRE Description
0 TDR contains valid transmit data
TDRE is cleared to 0 when software reads TDRE after it has been set to 1, then
writes 0 in TDRE or the DMAC or DTC writes data in TDR
1 TDR does not contain valid transmit data (initial value)
TDRE is set to 1 when the chip is power-on reset or enters standby mode, the TE
bit in the serial control register (SCR) is cleared to 0, or TDR contents are loaded
into TSR, so new data can be written in TDR