DS232BQ Version 1.8

© Future Technology Devices Intl. Ltd. 2005

Page 15 of 25

FT232BQ USB UART ( USB - Serial) I.C.

7.2 EEPROM Configuration

Figure 6

EEPROM Configuration

EECS

EEDATA

32

FT232BM

EESK

1

2

2

CS

SK

DIN

DOUT

GND

NC

NC

VCC

EEPROM - 93C46 / 56 / 66

1

3

4

5

6

7

8

VCC

10k

2k2

VCC

Figure 6 illustrates how to connect the FT232BQ to the

93C46 (93C56 or 93C66) EEPROM. EECS (pin 32) is directly

connected to the chip select (CS) pin of the EEPROM. EESK

(pin 1) is directly connected to the clock (SK) pin of the

EEPROM. EEDATA (pin 2) is directly connected to the Data

In (Din) pin of the EEPROM. There is a potential condition

whereby both the Data Output (Dout) of the EEPROM can

drive out at the same time as the EEDATA pin of the FT232BQ.

To prevent potential data clash in this situation, the Dout of the

EEPROM is connected to EEDATA of the FT232BQ via a 2.2K

resistor.

Following a power-on reset or a USB reset, the FT232BQ will

scan the EEPROM to find out (a) if an EEPROM is attached

to the Device and (b) if the data in the device is valid. If both

of these are the case, then the FT232BQ will use the data in

the EEPROM, otherwise it will use its built-in default values.

When a valid command is issued to the EEPROM from the

FT232BQ, the EEPROM will acknowledge the command by

pulling its Dout pin low. In order to check for this condition,

it is necessary to pull Dout high using a 10K resistor. If the

command acknowledge doesn’t happen then EEDATA will be

pulled high by the 10K resistor during this part of the cycle

and the device will detect an invalid command or no EEPROM

present.

There are two varieties of these EEPROM’s on the market – one is configured as being 16 bits wide, the other is

configured as being 8 bits wide. These are available from many sources such as Microchip, STMicro, ISSI etc. The

FT232BQ requires EEPROM’s with a 16-bit wide configuration such as the Microchip 93LC46B device. The EEPROM

must be capable of reading data at a 1Mb clock rate at a supply voltage of 4.35V to 5.25V. Most available parts are

capable of this.

Check the manufacturers data sheet to find out how to connect pins 6 and 7 of the EEPROM. Some devices specify

these as no-connect, others use them for selecting 8 / 16 bit mode or for test functions. Some other parts have their

It is possible to “share” the EEPROM between the FT232BQ and another external device such as an MCU. However,

this can only be done when the FT232BQ is in its reset condition as it tri-states its EEPROM interface at that time. A

typical configuration would use four bit’s of an MCU IO Port. One bit would be used to hold the FT232BQ reset (using

RESET#) on power-up, the other three would connect to the EECS, EESK and EEDATA pins of the FT232BQ in

order to read / write data to the EEPROM at this time. Once the MCU has read / written the EEPROM, it would take

RESET# high to allow the FT232BQ to configure itself and enumerate over USB.

FT232BQ