Matrix LED Display Driver

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7

Bit Transfer

One data bit is transferred during each clock pulse.

The data on the SDA line must remain stable while SCL

is high (Figure 4).

Acknowledge

The acknowledge bit is a clocked 9th bit that the recipi-

ent uses to handshake receipt of each byte of data

(Figure 5). Thus, each byte transferred effectively

requires 9 bits. The master generates the 9th clock

pulse, and the recipient pulls down SDA during the

acknowledge clock pulse, such that the SDA line is sta-

ble low during the high period of the clock pulse. When

the master is transmitting to the MAX6953, the

MAX6953 generates the acknowledge bit because the

MAX6953 is the recipient. When the MAX6953 is trans-

mitting to the master, the master generates the

acknowledge bit because the master is the recipient.

Slave Address

The MAX6953 has a 7-bit-long slave address (Figure

6). The eighth bit following the 7-bit slave address is

the R/W bit. It is low for a write command, high for a

read command.

The first 3 bits (MSBs) of the MAX6953 slave address

are always 101. Slave address bits A3, A2, A1, and A0

are selected by the address input pins AD1 and AD0.

These two input pins may be connected to GND, V+,

SDA, or SCL. The MAX6953 has 16 possible slave

addresses (Table 3) and therefore a maximum of 16

MAX6953 devices may share the same interface.

Message Format for Writing

A write to the MAX6953 comprises the transmission of

the MAX6953's slave address with the R/W bit set to

zero, followed by at least 1 byte of information. The first

byte of information is the command byte, which deter-

mines which register of the MAX6953 is to be written by

the next byte, if received. If a STOP condition is detect-

ed after the command byte is received, then the

MAX6953 takes no further action (Figure 7) beyond

storing the command byte.

Any bytes received after the command byte are data

bytes. The first data byte goes into the internal register of

the MAX6953 selected by the command byte (Figure 8).

If multiple data bytes are transmitted before a STOP

condition is detected, these bytes are generally stored

in subsequent MAX6953 internal registers because the

command byte address generally autoincrements

(Table 4) (Figure 9).

Message Format for Reading

The MAX6953 is read using the MAX6953's internally

stored command byte as address pointer, the same

way the stored command byte is used as address

pointer for a write. The pointer generally autoincre-

ments after each data byte is read using the same rules

as for a write (Table 4). Thus, a read is initiated by first

configuring the MAX6953's command byte by perform-

ing a write (Figure 7). The master can now read n con-

secutive bytes from the MAX6953, with the first data

byte being read from the register addressed by the ini-

tialized command byte (Figure 9). When performing

STOP

CONDITION

START

CONDITION

REPEATED START

CONDITION

SDA

SCL

START

CONDITION

Figure 2. 2-Wire Serial Interface Timing Details