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AN232R-01 Bit Bang Modes for the FT232R and FT245R

Copyright © 2006 Future Technology Devices International Ltd.

1.4

CBUS Bit Bang Mode

The FT232R supports a new type of Bit Bang mode on the CBUS pins. The CBUS Bit Bang mode

must be configured in the FT232R EEPROM and then enabled with a FT_SetBitMode command to

function. It is not available on the FT245R.

When CBUS Bit Bang mode is enabled the CBUS pins are configured as follows:

FT232RL

Pin

Number

FT232RQ

Pin

Number

Signal

Type

Description

23

22

C0

Input/Output

CBUS Bit Bang Bit 0

22

21

C1

Input/Output

CBUS Bit Bang Bit 1

13

10

C2

Input/Output

CBUS Bit Bang Bit 2

14

11

C3

Input/Output

CBUS Bit Bang Bit 3

The FT_SetBitMode and FT_GetBitMode D2XX commands are required to communicate with

CBUS Bit Bang. Since these functions allow only a single byte to be sent or received, this version

of Bit Bang is much slower than the Asynchronous and Synchronous Bit Bang types when used to

transfer large buffers of data with FT_Write and FT_Read, but it does provide an additional 4 IO

pins for the FT232R. The data transfer rate is limited by USB frames.

The D2XX commands required to use CBUS Bit Bang mode are listed below:

D2XX Function

Description

FT_SetBitMode

CBUS Bit Bang mode is enabled using the FT_SetBitMode command. A

value of 0x20 will enable it and a value of 0x00 will reset the device mode.

Note that the CBUS pins must also be configured for CBUS Bit Bang in the

FT232R EEPROM.

FT_SetBitMode also provides the means to write data to the CBUS pins.

The upper nibble of the Mask parameter controls which pins are inputs or

outputs, while the lower nibble controls which of the outputs are high or low.

FT_GetBitMode

FT_GetBitMode returns the instantaneous value of the pins. A single byte

will be returned where the lower nibble contains the current values of the

pins, both those which are inputs and those which are outputs.

For example:

Set all pins to output with bit 0 high:

FT_SetBitMode(Handle, 0xF1, 0x20)

Set bits 0 and 1 to input, bits 2 and 3 to output and make bits 2 and 3

high:

FT_SetBitMode(Handle, 0xCC, 0x20)

Read pins:

FT_GetBitMode(Handle, Data) where the lower nibble is given by (Data AND

0x0F)

Full descriptions of these functions are available in the D2XX Programmer's Guide.

Code examples can be downloaded from http://www.ftdichip.com/Projects/CodeExamples.htm.