CHAPTER 10 SERIAL INTERFACE FUNCTION
User’s Manual U13850EJ4V0UM
342
(b) Communication Operations
In the 3-wire variable-length serial I/O mode, data is transmitted and received in 8 to 16-bit units, and is
specified by setting bits 3 to 0 (BSEL3 to BSEL0) of variable-length serial setting register 4 (CSIB4). Each
bit of data is transmitted or received in synchronization with the serial clock.
After transfer of all bits is completed, SIC4 stops operation automatically and the interrupt request flag
(INTCSI4) is set.
Bits 6 and 5 (CMODE and DMODE) of variable-length serial setting register 4 (CSIB4) can change the
attribute of the serial clock (SCK4) and the phases of serial data (SI4 and SO4).
Figure 10-57. Timing of 3-Wire Variable-Length Serial I/O Mode
SCK4 (CMODE = 0)
SIO4 (write)
SO4 (DMODE = 1)
INTCSI4
SCK4 (CMODE = 1)
SO4 (DMODE = 0)
Remark
An arrow shows the SI4 data fetch timing.
When CMODE = 0, the serial clock (SCK4) stops at the high level during the operation stop, and outputs the
low level during a data transfer operation. When CMODE = 1, on the other hand, SCK4 stops at the low
level during the operation stop and outputs the high level during a data transfer operation.
The phases of the SO4 output timing and the S14 fetch timing can be shifted half a clock by setting DMODE.
However, the interrupt signal (INTCSI4) is generated at the final edge of the serial clock (SCK4), regardless
the setting of CSIB4.
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