71M6521DE/71M6521FE
Energy Meter IC
DATASHEET
JANUARY 2008
Three-Wire EEPROM Interface
A 500kHz three-wire interface, using SDATA, SCK, and a DIO pin for CS is available. The interface is selected with
DIO_EEX=3. The same 2-wire EECTRL register is used, except the bits are reconfigured, as shown in Table 58. When EECTRL
is written, up to 8 bits from EEDATA are either written to the EEPROM or read from the EEPROM, depending on the values of
the EECTRL bits.
Control
Name
WFR
Read/Write
Description
Bit
Wait for Ready. If this bit is set, the trailing edge of BUSY will be delayed
until a rising edge is seen on the data line. This bit can be used during
the last byte of a Write command to cause the INT5 interrupt to occur
when the EEPROM has finished its internal write sequence. This bit is
ignored if HiZ=0.
7
W
R
Asserted while serial data bus is busy. When the BUSY bit falls, an INT5
interrupt occurs.
6
BUSY
Indicates that the SD signal is to be floated to high impedance immedi-
ately after the last SCK rising edge.
5
4
HiZ
RD
W
W
Indicates that EEDATA is to be filled with data from EEPROM.
Specifies the number of clocks to be issued. Allowed values are 0
through 8. If RD=1, CNT bits of data will be read MSB first, and right
justified into the low order bits of EEDATA. If RD=0, CNT bits will be sent
MSB first to EEPROM, shifted out of EEDATA’s MSB. If CNT is zero,
SDATA will simply obey the HiZ bit.
3-0
CNT[3:0]
W
Table 58: EECTRL bits for 3-wire interface
The timing diagrams in Figure 9 through Figure 13 describe the 3-wire EEPROM interface behavior. All commands begin when
the EECTRL register is written. Transactions start by first raising the DIO pin that is connected to CS. Multiple 8-bit or less
commands such as those shown in Figure 9 through Figure 13 are then sent via EECTRL and EEDATA. When the transaction
is finished, CS must be lowered. At the end of a Read transaction, the EEPROM will be driving SDATA, but will transition to
HiZ (high impedance) when CS falls. The firmware should then immediately issue a write command with CNT=0 and HiZ=0 to
take control of SDATA and force it to a low-Z state.
EECTRL Byte Written
INT5
CNT Cycles (6 shown)
Write -- No HiZ
SCLK (output)
D7
D6
D5
D4
D3
D2
SDATA (output)
SDATA output Z
BUSY (bit)
(LoZ)
Figure 9: 3-Wire Interface. Write Command, HiZ=0.
v1.0
© 2005-2008 TERIDIAN Semiconductor Corporation
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