71M6521DE/71M6521FE
Energy Meter IC
DATASHEET
JANUARY 2008
Connecting Three-Wire EEPROMs
µWire EEPROMs and other compatible devices should be connected to the DIO pins DIO4 and DIO5, as shown in Figure 34.
DIO5 connects to both the DI and DO pins of the three-wire device. The CS pin must be connected to a vacant DIO pin of the
71M6521DE/FE. A pull-up resistor of roughly 10kΩ to V3P3D (to ensure operation in BROWNOUT mode) should be used for
the DI/DO signals, and the CS pin should be pulled down with a resistor to prevent that the three-wire device is selected on
power-up, before the 71M6521DE/FE can establish a stable signal for CS. The DIO_EEX register in I/O RAM must be set to 10
in order to convert the DIO pins DIO4 and DIO5 to uWire pins. The pull-up resistor for DIO5 may not be necessary.
V3P3D
71M6521
10kΩ
10kΩ
EEPROM
SCLK
DI
DIO4
DIO5
DIOn
DO
CS
Figure 34: Three-Wire EEPROM Connection
UART0 (TX/RX)
The RX pin should be pulled down by a 10kΩ resistor and additionally protected by a 100pF ceramic capacitor, as shown in
Figure 35.
71M6521E
10kΩ
100pF
RX
RX
TX
TX
Figure 35: Connections for the RX Pin
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