
HARDWARE
1-104
7470/7471/7477/7478 GROUP USER’S MANUAL
1.13 Serial I/O
(3) Serial I/O mode register (SM: Address 00DC16)
The Serial I/O mode register selects a state of the clock or port to be used for a data transfer.
Figure 1.13A.9 shows a structure of the Serial I/O mode register.
Fig. 1.13A.9 Structure of Serial I/O mode register
b7 b6 b5 b4 b3 b2 b1 b0
Serial I/O mode register (SM) [Address
B
At reset
RW
Serial I/O mode register (7470/7471 group)
0, 1
2
3
4
5
6
7
0
Name
Function
0 0 : f(XIN)/8 or f(XCIN)/8
b1 b0
Internal clock
selection bits
Synchronous clock
selection bit
Serial I/O port
selection bit
SRDY signal output
selection bit
SRDY signal
selection bit
Serial I/O byte specify
mode selection bit
P15/SOUT, SRDY output
structure selection bit
0 1 : f(XIN)/16 or f(XCIN)/16
1 0 : f(XIN)/32 or f(XCIN)/32
1 1 : f(XIN)/512 or f(XCIN)/512
(Note)
0 : External clock
1 : Internal clock
0 : Ordinary I/O port
(P15, P16)
1 : Serial I/O port (SOUT, CLK pin)
0 : Ordinary I/O port(P1 7)
1 : SRDY signal output pin
0 : SRDY signal
1 : SARDY signal
0 : Ordinary mode
1 : Byte specify mode
0 : CMOS output
1 : N-channel open-drain
output
Since the 7470 group is not provided with the sub-clock
generating circuit, do not select f(X
Note:
00DC16]
CIN
).