78M6612 Data Sheet
DS_6612_001
1.5.10 EEPROM Interface
The 78M6612 provides hardware support for a two-pin or a three-pin EEPROM interface. The EEPROM
interface uses the EECTRL and EEDATA registers for communication.
1.5.10.1 Two-Pin EEPROM Interface
The dedicated 2-pin serial interface communicates with external EEPROM devices. The interface is
multiplexed onto pins DIO4 (SCK) and DIO5 (SDA) controlled by the I/O RAM bits DIO_EEX[1:0] (see
the I/O RAM Table). Set DIO_EEX[1:0] = 01 to select the two-wire EEPROM interface. The MPU
communicates with the interface through two SFR registers: EEDATA and EECTRL. If the MPU wishes to
write a byte of data to EEPROM, it places the data in EEDATA and then writes the ‘Transmit’ command
(CMD = 0011) to EECTRL. This initiates the transmit operation. The transmit operation is finished when
the BUSY bit falls. Interrupt INT5 is also asserted when BUSY falls. The MPU can then check the
RX_ACK bit to see if the EEPROM acknowledged the transmission.
A byte is read by writing the Receive command (CMD[3:0] = 0001) to EECTRL and waiting for the BUSY
bit to fall. Upon completion, the received data is in EEDATA. The serial transmit and receive clock is 78
kHz during each transmission, and the clock is held in a high state until the next transmission. The bits
in EECTRL are shown in Table 41.
The EEPROM interface can also be operated by controlling the DIO4 and DIO5 pins directly
(“bit-banging”). However, controlling DIO4 and DIO5 directly is discouraged, because it may tie
up the MPU to the point where it may become too busy to process interrupts.
Table 41: EECTRL Status Bits
Read
Status
Bit
Reset
State
Name
/
Polarity Description
Write
7
6
5
4
ERROR
BUSY
R
R
R
R
0
0
1
1
Positive 1 when an illegal command is received.
Positive 1 when serial data bus is busy.
RX_ACK
TX_ACK
Negative 0 indicates that the EEPROM sent an ACK bit.
Negative 0 indicates when an ACK bit has been sent to
the EEPROM.
CMD
Operation
0000
No-op. Applying the no-op
command will stop the I2C clock
(SCK, DIO4). Failure to issue the
no-op command will keep the SCK
signal toggling.
Positive,
see
CMD
0001
Receive a byte from EEPROM and
send ACK.
CMD[3:0]
3-0
W
0
0011
0101
Transmit a byte to EEPROM.
Issue a ‘STOP’ sequence.
Table
0110
Receive the last byte from
EEPROM, do not send ACK.
1001
Issue a ‘START’ sequence.
Others No Operation, set the ERROR bit.
46
Rev. 1.2
TERIDIAN [ TERIDIAN SEMICONDUCTOR CORPORATION ]
