MCP23009ESS datasheet(9/50 Pages) MICROCHIP

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DS22121B-page 9

MCP23009/MCP23S09

1.4

Multi-bit Address Decoder

The ADDR pin is used to set the slave address of the

MCP23009 (I2C only) to allow up to eight devices on

the bus using only a single pin. Typically, this would

require three pins.

The multi-bit Address Decoder employs a basic FLASH

ADC architecture (Figure 1-4). The seven comparators

generate 8 unique values based on the analog input.

This value is converted to a 3-bit code which

corresponds to the address bits (A2, A1, A0) in the

serial OPCODE.

Sequence

Operation

(see

Figure 1-5

for

timings):

Upon power up (after VDD stabilizes) the module

becomes active after time tADEN. Note, the

analog value on the ADDR pin must be stable

before this point to ensure accurate address

assignment.

The 3-bit address is latched after tADDRLAT.

The module powers down after the first rising

edge of the serial clock is detected (tADDIS).

Once the address bits are latched, the device will keep

the slave address until a POR or reset condition

occurs.

1.4.1

CALCULATING VOLTAGE ON ADDR

When calculating the required voltage on the ADDR pin

(V2), the set point should be the mid-point of the LSb of

the ADC.

The examples in Figure 1-2 and Figure 1-3 show how

to determine the mid point voltage (V2) and the range

of voltages based on a voltage divider circuit. The

maximum

tolerance

20%,

however,

recommended to use 5% tolerance worst case (10%

total tolerance).

FIGURE 1-2:

VOLTAGE DIVIDER EXAMPLE

VDD

MCP23009 Only

VDD

VSS

ADDR

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