FT245BQ USB FIFO ( USB - Parallel ) I.C.
7.2 EEPROM Configuration
Figure 6
EEPROM Configuration
Figure 6 illustrates how to connect the FT245BQ 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
FT245BQ. To prevent potential data clash in this situation,
the Dout of the EEPROM is connected to EEDATA of the
FT245BQ via a 2.2 K resistor.
FT245BQ
32
1
EECS
EESK
2
EEDATA
Following a power-on reset or a USB reset, the FT245BQ 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 FT245BQ 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
FT245BQ, 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.
VCC
EEPROM - 93C46 / 56 / 66
1
8
7
6
5
CS
VCC
NC
2
3
SK
2k2
DIN
DOUT
NC
4
GND
VCC
10k
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, ST Micro, ISSI etc. The
FT245BQ 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
pinout rotated by 90o so please select the required part and its options carefully.
It is possible to “share” the EEPROM between the FT245BQ and another external device such as an MCU. However,
this can only be done when the FT245BQ is in its reset condition as it tri-states its EEPROM interface at that time. A
typical configuration would use four bits of an MCU IO Port. One bit would be used to hold the FT245BQ reset (using
RESET#) on power-up, the other three would connect to the EECS, EESK and EEDATA pins of the FT245BQ 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 FT245BQ to configure itself and enumerate over USB.
DS245BQ Version 1.7
© Future Technology Devices Intl. Ltd. 2005
Page 16 of 24
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