h8s-2172 Renesas Electronics Corporation., h8s-2172 Datasheet - Page 347

• Manufacturer Part Number: h8s-2172
• Description: Renesas 16-bit Single-chip Microcomputer H8s Family H8s-2100 Series
• Manufacturer: Renesas Electronics Corporation.

11.6
11.6.1
SCI operation can be disabled or enabled using the module stop control register. The initial setting
is for SCI operation to be halted. Register access is enabled by clearing module stop mode. For
details, refer to section 16, Power-Down Modes.
11.6.2
The TDRE flag in SSR is a status flag that indicates that transmit data has been transferred from
TDR to TSR. When the SCI transfers data from TDR to TSR, the TDRE flag is set to 1.
Data can be written to TDR regardless of the state of the TDRE flag. However, if new data is
written to TDR when the TDRE flag is cleared to 0, the data stored in TDR 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 TDR.
11.6.3
• Transmission
• Reception
Operation should be stopped (by clearing TE, TIE, and TEIE to 0) before making a module
stop mode or software standby mode transition. TSR, TDR, and SSR are reset. The output pin
states in module stop mode or software standby mode depend on the port settings, and become
high-level output after the relevant mode is cleared. If a transition is made during transmission,
the data being transmitted will be undefined.
When transmitting without changing the transmit mode after the relevant mode is cleared,
transmission can be started by setting TE to 1 again, and performing the following sequence:
SSR read → TDR write → TDRE clearance. To transmit with a different transmit mode after
clearing the relevant mode, the procedure must be started again from initialization.
Figure 11.9 shows a sample flowchart for mode transition during transmission.
Receive operation should be stopped (by clearing RE to 0) before making a module stop mode
or software standby mode transition. RSR, RDR, and SSR are reset. If a transition is made
during reception, the data being received will be invalid.
To continue receiving without changing the reception mode after the relevant mode is cleared,
set RE to 1 before starting reception. To receive with a different receive mode, the procedure
must be started again from initialization.
Figure 11.10 shows a sample flowchart for mode transition during reception.
Usage Notes
Module Stop Mode Setting
Relation between Writes to TDR and the TDRE Flag
Operation in Case of Mode Transition
Rev. 2.00, 03/04, page 315 of 534