
29
3819 Group
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
MITSUBISHI MICROCOMPUTERS
Table GA-2. P6
7
/S
RDY1
/CS selection
(2.4) When Selecting the External Clock
When selecting the external clock, the internal clock and the set-
ting of transfer interval with the serial I/O automatic transfer
interval register are invalid, but the serial I/O output pin S
OUT1
and
the internal transfer clock can be controlled from the outside by
setting the S
RDY1
pin to the CS (input) pin.
When the CS input is “L”, the S
OUT1
pin and the internal transfer
clock are enabled.
When the CS input is “H”, the S
OUT1
pin goes to high impedance
state and the internal transfer clock goes to “H”.
Select the function of the P6
7
/S
RDY1
/CS/S
CLK12
with the following
registers (refer to Table GA-2):
G
the bit 4 (SC1
4
) and the bit 6 (SC1
6
) of the serial I/O1 control
register
G
the bit 0 (SIOAC
0
) of the serial I/O automatic transfer control
register
Switch the CS pin from “L” to “H” or from “H” to “L” during “H” of the
transfer clock (S
CLK11
input) after transferring 1-byte data.
When selecting the external clock, set the external clock to “L” af-
ter 9 cycles or more of the internal clock
φ
after setting the start
bit. After transferring 1-byte data, leave 11 cycles or more of the
internal clock
φ
free for the transfer interval.
OUT
pin will not go to
high impedance state, even after transfer is completed.
When not using the CS input, or when CS is “L”, control the exter-
nal clock because the data in the serial I/O register will continue to
shift while the external clock is input, even after the completion of
automatic transfer (Note that the automatic transfer interrupt re-
quest bit is set and the bit 1 of the serial I/O automatic transfer
register is cleared at the point when the specified number of bytes
of data have been transferred.)
SC1
6
0
SC1
4
0
1
SIOAC
0
0
1
P6
7
/S
RDY1
/CS
P6
7
S
RDY1
CS
Note :
SC1
4
: S
RDY1
output selection bit
SC1
6
: Synchronous clock selection bit
SIOAC
0
: Automatic transfer control bit
Fig. GA-10 Timing during serial I/O automatic transfer (external clock selected)
X
Bit 1 write signal of serial I/O
automatic transfer control
register
Serial I/O output
S
OUT
Serial I/O input
S
IN
Note:
Data marked with X is invalid.
Bit 1 of serial I/O automatic
transfer control register
Write signal from RAM to
serial I/O1 register
Write signal from serial I/O1
register to RAM
Transfer clock
(internal)
Data pointer
CS
n-1
n
DO
0
X
Transfer clock
S
CLK
input
External input
X
DO
1
DO
2
DO
3
DO
4
DO
5
DO
6
DO
7
DI
0
DI
1
DI
2
DI
3
DI
4
DI
5
DI
6
DI
7
X
X
X