24C04A
4.0
SLAVE ADDRESS
5.0
BYTE PROGRAM MODE
The chip address inputs A1 and A2 must be externally
connected to either VCC or ground (VSS), thereby
assigning a unique address to each device. A0 is not
used on the 24C04A and must be connected to either
VCC or VSS. Up to four 24C04A devices may be con-
nected to the bus. Chip selection is then accomplished
through software by setting the bits A1 and A2 of the
slave address to the corresponding hard-wired logic lev-
els of the selected 24C04A. After generating a START
condition, the bus master transmits the slave address
consisting of a 4-bit device code (1010), followed by the
chip address bits A0, A1 and A2. The seventh bit of that
byte (A0) is used to select the upper block (addresses
100—1FF) or the lower block (addresses 000—0FF) of
the array.
In this mode, the master sends addresses and one
data byte to the 24C04A.
Following the START signal from the master, the device
code (4-bits), the slave address (3-bits), and the R/W
bit, which is logic LOW, are placed onto the bus by the
master. This indicates to the addressed 24C04A that a
byte with a word address will follow after it has gener-
ated an acknowledge bit. Therefore the next byte trans-
mitted by the master is the word address and will be
written into the address pointer of the 24C04A. After
receiving the acknowledge, the master device trans-
mits the data word to be written into the addressed
memory location. The 24C04A acknowledges again
and the master generates a STOP condition. This ini-
tiates the internal programming cycle (Figure 6-1).
The eighth bit of the slave address determines if the
master device wants to read or write to the 24C04A
(Figure 4-1).
The 24C04A monitors the bus for its corresponding
slave address all the time. It generates an acknowl-
edge bit if the slave address was true and it is not in a
programming mode.
FIGURE 4-1: SLAVE ADDRESS
ALLOCATION
START
READ/WRITE
SLAVE ADDRESS
R/W
A
1
0
1
0
A2
A1
A0
2004 Microchip Technology Inc.
DS11183F-page 5
ROCHESTER [ Rochester Electronics ]
