Datasheet

Section 19 Synchronous Serial Communication Unit (SSU)
Page 1050 of 1384 R01UH0310EJ0500 Rev. 5.00
Sep 25, 2012
H8S/2426, H8S/2426R, H8S/2424 Group
19.3.8 SS Receive Data Registers 0 to 3 (SSRDR0 to SSRDR3)
SSRDR is an 8-bit register that stores receive data. When 8-bit data length is selected by bits
DATS1 and DATS0 in SSCRL, SSRDR0 is valid. When 16-bit data length is selected, SSRDR0
and SSRDR1 are valid. When 24-bit data length is selected, SSRDR0, SSRDR1, and SSRDR2 are
valid. When 32-bit data length is selected, SSRDR0 to SSRDR3 are valid. Be sure not to access to
invalid SSRDR.
When the SSU has received 1-byte data, it transfers the received serial data from SSTRSR to
SSRDR where it is stored. After this, SSTRSR is ready for reception. Since SSTRSR and SSRDR
function as a double buffer in this way, consecutive receive operations can be performed.
Read SSRDR after confirming that the RDRF bit in SSSR is set to 1.
SSRDR is a read-only register, therefore, cannot be written to by the CPU.
Table 19.3 Correspondence Between DATS Bit Setting and SSRDR
DATS[1:0] (SSCRL[1:0])
SSRDR 00 01 10 11 (Setting Invalid)
0 Valid Valid Valid Valid
1 Invalid Valid Valid Valid
2 Invalid Invalid Valid Valid
3 Invalid Invalid Valid Invalid
19.3.9 SS Shift Register (SSTRSR)
SSTRSR is a shift register that transmits and receives serial data.
When data is transferred from SSTDR to SSTRSR, bit 0 of transmit data is bit 0 in the SSTDR
contents (MLS = 0: LSB first communication) and is bit 7 in the SSTDR contents (MLS = 1: MSB
first communication). The SSU transfers data from the LSB (bit 0) in SSTRSR to the SSO pin to
perform serial data transmission.
In reception, the SSU sets serial data that has been input via the SSI pin in SSTRSR from the LSB
(bit 0). When 1-byte data has been received, the SSTRSR contents are automatically transferred to
SSRDR. SSTRSR cannot be directly accessed by the CPU.