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www.fairchildsemi.com

FM3565 Rev. A.1

Functional Description

The FM3565 block diagram is shown in Figure 1.

Operational Modes

During standard operation, the device will pass data to the Y-Port

either from the I-Port or from one of the internally stored Non-

Volatile Register values.

The I-port values are generated from the motherboard of the

system and may be hardwired or driven by another device. Pull-

up resistors are provided on the device to accommodate this

device being driven by open-drain output drivers. The device

expects standard CMOS input signals. The outputs (Y0-Y4)

operate in the open-drain mode. The OVRD (override) input, when

set to 0, will cause all the outputs to be set to 0. The WP signal, if

set to logic 1, will prevent data from being written to the non-volatile

register.

The functioning of this device is described by the truth table in

Table 1.

Output Port: Y0-Y4

The output port is an open-drain output to allow for easy connec-

tion to devices running at different voltage levels. The port is

always active and either passes the value on the I-Port or data

from one of the internal non-volatile registers (SOPRA/B). Chang-

ing the Mux Path is accomplished using the external hardware

controls – OVRD, MUXSEL, and A/B.

Register Description

The FM3550/60 has 3 registers in total. These registers are made

up of a combination of read-only, write-only and read/write bits.

The two registers are listed below.

Serial Output Port Register A(SOPRA) Address: 00H - A read/

write register that contains the new value of SOPRA.

Serial Output Port Register B(SOPRB) Address: 01H - A read/

write register that contains the new value for SOPRB.

Parallel Input Port Register (PIPR) Address: 02H - A read-only

register that is loaded with the 5-bit value of the I-Port.

Serial Output Port Register (SOPR)

(Address 000b and 001b)

MXSB MXSA

Data Field

0

0

I5

0

I3I2I1

I0

b7

b6

b5

b4

b3

b2

B1

b0

b7-b6 - Multiplexer Select Bits (MXSB,MXSA)

00 - Multiplexer passes the SOPR(A).

01 - Multiplexer passer the SOPR(B).

10 - Multiplexer defaults to passing the I-Port Value.

b5, b3-b0 - Data Field. New value to be output through the

multiplexer.

Parallel Input Port Register (PIPR)

(Address 002b)

Address Field

Data Field

0

0

0

I4

I3I2I1

I0

b7

b6

b5

b4

b3

b2

B1

b0

b7-b5 - Address field. Value is always 000

b4-b0 - Data Field. Value is equal to the value on the I-Port.

The external Port Register captures the value on the I-Port. Data

is latched into this register on the first clock after a start condition

is seen. This insures that a valid value will always be in this register

if it is read. This register is a-read only register with respect to the

IIC port.