3-WIRE SERIAL E
2
PROM
Rev.7.0
_00
S-93C76A
Seiko Instruments Inc.
15
3-Wire Interface (Direct Connection between DI and DO)
There are two types of serial interface configurations: a 4-wire interface configured using the CS, SK, DI, and DO pins,
and a 3-wire interface that connects the DI input pin and DO output pin.
When the 3-wire interface is employed, a period in which the data output from the CPU and the data output from the
serial memory collide may occur, causing a malfunction. To prevent such a malfunction, connect the DI and DO pins
of the S-93C76A via a resistor (10 kΩ to 100 kΩ) so that the data output from the CPU takes precedence in being input
to the DI pin (refer to Figure 13).
CPU
DI
SIO
DO
S-93C76A
R: 10 kΩ to 100 kΩ
Figure 13 Connection of 3-Wire Interface
Input Pin and Output Pin
1. Connection of input pins
All the input pins of the S-93C76A employ a CMOS structure, so design the equipment so that high impedance will
not be input while the S-93C76A is operating. Especially, deselect the CS input (a low level) when turning on / off
power and during standby. When the CS pin is deselected (a low level), incorrect data writing will not occur.
Connect the CS pin to GND via a resistor (10 kΩ to 100 kΩ pull-down resistor). To prevent malfunction, it is
recommended to use equivalent pull-down resistors for pins other than the CS pin.
2. Equivalent circuit of input and output pin
The following shows the equivalent circuits of input pins of the S-93C76A. None of the input pins incorporate pull-
up and pull-down elements, so special care must be taken when designing to prevent a floating status.
Output pins are high-level / low-level / high-impedance tri-state outputs. The TEST pin is disconnected from the
internal circuit by a switching transistor during normal operation. As long as the absolute maximum rating is
satisfied, the TEST pin and internal circuit will never be connected.
