HD64F38602R Datasheet, PDF (325/552 Pages) Renesas Technology Corp – Renesas 16-Bit Single-Chip Microcomputer

Section 15 Synchronous Serial Communication Unit (SSU)
15.3.6 SS Receive Data Register (SSRDR)
SSRDR is an 8-bit register that stores received serial data. When the SSU has received one byte of
serial data, it transfers the received serial data from SSTRSR and the data is stored. After this,
SSTRSR is receive-enabled. As SSTRSR and SSRDR function as a double buffer in this way,
continuous receive operations are possible. SSRDR is a read-only register and cannot be written to
by the CPU. SSRDR is initialized to H'00.
15.3.7 SS Transmit Data Register (SSTDR)
SSTDR is an 8-bit register that stores serial data for transmission. SSTDR can be read or written
to by the CPU at all times. When the SSU detects that SSTRSR is empty, it transfers the transmit
data written in SSTDR to SSTRSR and starts serial transmission. If the next transmit data has
already been written to SSTDR during serial transmission, continuous serial transmission is
possible. SSTDR is initialized to H'00.
15.3.8 SS Shift Register (SSTRSR)
SSTRSR is a shift register that transmits and receives serial data. When transmit data is transferred
from SSTDR to SSTRSR, bit 0 in SSTDR is transferred to bit 0 in SSTRSR while the MLS bit in
SSMR is 0 (LSB-first transfer) and bit 7 in SSTDR is transferred to bit 0 in SSTRSR while the
MLS bit in SSMR is 1 (MSB-first transfer). SSTRSR cannot be directly accessed by the CPU.
15.4 Operation
15.4.1 Transfer Clock
Transfer clock can be selected from eight internal clocks and an external clock. When this module
is used, the SSCK pin must be selected as a serial clock by setting the SCKS bit in SSCRH to 1.
When the MSS bit in SSCRH is 1, an internal clock is selected and the SSCK pin is in the output
state. If transfer is started, the SSCK pin outputs clocks of the transfer rate set in the CKS2 to
CKS0 bits in SSMR. When the MSS bit is 0, an external clock is selected and the SSCK pin is in
the input state.
Rev. 3.00 May 15, 2007 Page 293 of 518
REJ09B0152-0300