HD643303x Hitachi, HD643303x Datasheet - Page 341

• Manufacturer Part Number: HD643303x
• Description: Hitachi Microcomputer
• Manufacturer: Hitachi

The CPU can always read and write SSR, but cannot write 1 in the TDRE, RDRF, ORER, PER,
and FER flags. These flags can be cleared to 0 only if they have first been read while set to 1. The
TEND and MPB flags are read-only bits that cannot be written.
SSR is initialized to H'84 by a reset and in standby mode.
Bit 7—Transmit Data Register Empty (TDRE): Indicates that the SCI has loaded transmit data
from TDR into TSR and the next serial transmit data can be written in TDR.
Bit 7
TDRE
0
1
Bit 6—Receive Data Register Full (RDRF): Indicates that RDR contains new receive data.
Bit 6
RDRF
0
1
Note: The RDR contents and RDRF flag are not affected by detection of receive errors or by
clearing of the RE bit to 0 in SCR. They retain their previous values. If the RDRF flag is still
set to 1 when reception of the next data ends, an overrun error occurs and receive data is
lost.
Description
TDR contains valid transmit data
[Clearing conditions]
Software reads TDRE while it is set to 1, then writes 0.
TDR does not contain valid transmit data
[Setting conditions]
The chip is reset or enters standby mode.
The TE bit in SCR is cleared to 0.
TDR contents are loaded into TSR, so new data can be written in TDR.
Description
RDR does not contain new receive data
[Clearing conditions]
The chip is reset or enters standby mode.
Software reads RDRF while it is set to 1, then writes 0.
The DMAC reads data from RDR.
RDR contains new receive data
[Setting condition]
When serial data is received normally and transferred from RSR to RDR.
326
(Initial value)
(Initial value)