ACE24AC04.08.16

Two-wire Serial EEPROM

VER 1.2

5

Figure 2: Timing diagram for output acknowledge

Device Addressing

The 2-wire serial bus protocol mandates an 8 bits device address word after a start bit condition to

invoke valid read or write command. The first four most significant bits of the device address must be

1010, which is common to all serial EEPROM devices. The next three bits are device address bits.

These three device address bits (5

th

, 6

th

and 7

th

) are to match with the external chip select/address

pin states. If a match is made, the EEPROM device outputs an acknowledge signal after the 8th

read/write bit, otherwise the chip will go into standby mode. However, matching may not be needed

for some or all device address bits (5

th

, 6

th

and 7

th

) as noted below. The last or 8th bit is a read/write

command bit. If the 8th bit is at VIH then the chip goes into read mode. If a “0” is detected, the device

enters programming mode.

ACE24AC04 uses A2 (5

th

) and A1 (6

th

) device address bits. Only four ACE24AC04 devices can be

wired-OR on the same 2-wire bus. Their corresponding chip select address pins A2 and A1 must be

hard wired and coded from 00 (b) to 11 (b). Chip select address pin A0 is not used.

ACE24AC08 uses only A2 (5

th

) device address bit. Only two ACE24AC08 devices can be wired-OR

on the same 2-wire bus. Their corresponding chip select address pin A2 must be hard-wired and

coded from 0 (b) to 1 (b). Chip select address pins A1 and A0 are not used.

ACE24AC16 does not use any device address bit. Only one ACE24AC16 device can be used on the

on 2-wire bus. Chip Select address pins A2, A1, and A0 are not used.

Write Operations

A.

Byte Write

A byte write operation starts when a micro-controller sends a start bit condition, follows by a proper

EEPROM device address and then a write command. If the device address bits match the chip

select address, the EEPROM device will acknowledge at the 9

then send the rest of the lower 8 bits word address. At the 18

the 8-bit address word. The micro-controller will then transmit the 8 bit data. Following an

acknowledge signal from the EEPROM at the 27