8.2.7 Serial Status Register (SSR)—H'FFDC
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
Read/Write
R/(W)*
R/(W)*
R/(W)*
R/(W)*
R/(W)*
R
R
R/W
Note: * Software can write a “0” to clear the flags, but cannot write a “1” in these bits.
The SSR is an 8-bit register that indicates transmit and receive status. It is initialized to H'84 at a
reset and in the standby modes.
Bit 7—Transmit Data Register Empty (TDRE): This bit indicates when the TDR contents have
been transferred to the TSR and the next character can safely be written in the TDR.
Bit 7
TDRE
Description
0
To clear TDRE, the CPU must read TDRE after it has been set to “1,”
then write a “0” in this bit.
1
This bit is set to 1 at the following times:
(Initial value)
(1) When TDR contents are transferred to the TSR.
(2) When the TE bit in the SCR is cleared to “0.”
Bit 6—Receive Data Register Full (RDRF): This bit indicates when one character has been
received and transferred to the RDR.
Bit 6
RDRF
Description
0
To clear RDRF, the CPU must read RDRF after
(Initial value)
it has been set to “1,” then write a “0” in this bit.
1
This bit is set to 1 when one character is received without error and
transferred from the RSR to the RDR.
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