Usage Notes - Renesas Hitachi H8S/2194 Series Hardware Manual

23.5

Usage Notes

The following points should be noted when using the SCI1.
(1) Relation between Writes to TDR1 and the TDRE Flag
The TDRE flag in SSR1 is a status flag that indicates that transmit data has been transferred
from TDR1 to TSR. When the SCI transfers data from TDR1 to TSR, the TDRE flag is set
to 1.
Data can be written to TDR1 regardless of the state of the TDRE flag. However, if new data
is written to TDR1 when the TDRE flag is cleared to 0, the data stored in TDR1 will be lost
since it has not yet been transferred to TSR. It is therefore essential to check that the TDRE
flag is set to 1 before writing transmit data to TDR1.
(2) Operation when Multiple Receive Errors Occur Simultaneously
If a number of receive errors occur at the same time, the state of the status flags in SSR1 is as
shown in table 23.14. If there is an overrun error, data is not transferred from RSR to RDR1,
and the receive data is lost.
Table 23.14 State of SSR1 Status Flags and Transfer of Receive Data
SSR1 Status Flags
RDRF ORER FER
1 1 0
0 0 1
0 0 0
1 1 1
1 1 0
0 0 1
1 1 1
{
Notes: : Receive data is transferred from RSR to RDR1.
×: Receive data is not transferred from RSR to RDR1.
(3) Break Detection and Processing
When a framing error (FER) is detected, a break can be detected by reading the SI1 pin value
directly. In a break, the input from the SI1 pin becomes all 0s, and so the FER flag is set,
and the parity error flag (PER) may also be set.
Note that, since the SCI1 continues the receive operation after receiving a break, even if the
FER flag is cleared to 0, it will be set to 1 again.
(4) Sending a Break
The SO1 pin has a dual function as an I/O port whose direction (input or output) is
determined by PDR and PCR. This feature can be used to send a break.
Receive Data
Transfer
RSR → RDR1
PER
×
0
{
0
{
1
×
0
×
1
{
1
×
1
Receive Errors
Overrun error
Framing error
Parity error
Overrun error + framing error
Overrun error + parity error
Framing error + parity error
Overrun error + framing error + parity error
Rev. 2.0, 11/00, page 495 of 1037