HDTV Continuously Variable

Anti-Aliasing Filters

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11

Acknowledge Bit (ACK) and Not-Acknowledge Bit

(NACK)

Successful data transfers are acknowledged with an

acknowledge bit (ACK) or a not-acknowledge bit

(NACK). Both the master and the MAX7469/MAX7470

(slave) generate acknowledge bits. To generate an

acknowledge, the receiving device must pull SDA low

before the rising edge of the acknowledge-related clock

pulse (ninth pulse) and keep it low during the high period

of the clock pulse (Figure 4). To generate a NACK, the

receiver allows SDA to be pulled high before the rising

edge of the acknowledge-related clock pulse (ninth

pulse) and leaves it high during the high period of the

clock pulse. Monitoring the acknowledge bits allows for

detection of unsuccessful data transfers. An unsuccess-

ful data transfer happens if a receiving device is busy or

if a system fault has occurred. In the event of an unsuc-

cessful data transfer, the master should reattempt com-

munication at a later time.

The MAX7469/MAX7470 generate an acknowledge bit

when receiving an address or data by pulling SDA low

during the ninth clock pulse. When transmitting data

during a read, the MAX7469/MAX7470 do not drive

SDA during the ninth clock pulse (i.e., the external

pullups define the bus as a logic-high) so that the

receiver of the data can pull SDA low to acknowledge

receipt of data.

Slave Address

A bus master initiates communication with a slave device

by issuing a START condition, followed by the 7-bit slave

address (Figure 5). When idle, the MAX7469/MAX7470

wait for a START condition, followed by their slave

address. The serial interface compares each address bit

by bit, allowing the interface to power down and discon-

nect from SCL immediately if an incorrect address is

detected. After recognizing a START condition followed

by the correct address, the MAX7469/MAX7470 are

ready to accept or send data. The least significant bit

(LSB) of the address byte (R/W) determines whether the

master is writing to or reading from the MAX7469/

MAX7470 (R/W = 0 selects a write condition, R/W = 1

selects a read condition). After receiving the proper

address, the MAX7469/MAX7470 (slave) issue an ACK

by pulling SDA low for one clock cycle.

The MAX7469/MAX7470 slave address consists of 5

fixed bits, A6–A2 (set to 10010), followed by 2 pin-pro-

grammable bits, A1 and A0. The most significant

address bit (A6) is transmitted first, followed by the

remaining bits. Addresses A1 and A0 can also be driven

dynamically if required, but the values must be stable

when they are expected in the address sequence.

1

8

9

S

SDA

SCL

NOT ACKNOWLEDGE

ACKNOWLEDGE

SDA

SCL

1

0

1

0

A1

A0

0

R/W

MSB

LSB

ACK

.

Figure 4. Acknowledge and Not-Acknowledge Bits

Figure 5. Slave-Address Byte Definition