For the data to change there, has to be new data written and the Baud rate clock has to tick. If no new data is written to the device, the pins will hold the last value written.
When Asynchronous Bit Bang mode is enabled the IO signal lines are configured as follows:
FT232RL/ FT245RL Pin Number
|
FT232RQ/ FT245RQ Pin Number
|
Signal |
Type |
Description |
1
|
30
|
D0
|
Input/Output
|
Bit Bang Data Bus Bit 0
|
5
|
2
|
D1
|
Input/Output
|
Bit Bang Data Bus Bit 1
|
3
|
32
|
D2
|
Input/Output
|
Bit Bang Data Bus Bit 2
|
11
|
8
|
D3
|
Input/Output
|
Bit Bang Data Bus Bit 3
|
2
|
31
|
D4
|
Input/Output
|
Bit Bang Data Bus Bit 4
|
9
|
6
|
D5
|
Input/Output
|
Bit Bang Data Bus Bit 5
|
10
|
7
|
D6
|
Input/Output
|
Bit Bang Data Bus Bit 6
|
6
|
3
|
D7
|
Input/Output
|
Bit Bang Data Bus Bit 7
|
In the case of the FT232R, CBUS0/CBUS1/CBUS2/CBUS3 can be configured to bring out the internal RD# strobe and CBUS0/CBUS1 can be configured to bring out the internal WR# strobe when the device is in Asynchronous Bit Bang mode. This is the same as the Enhanced Asynchronous Bit Bang mode of the FT2232 device. Alternatively, the CBUS pins can be used to provide clock signals by setting the appropriate values in the EEPROM. The CBUS must be configured in the FT232R EEPROM. This option is not available for the FT245R.
FT232RL Pin Number
|
FT232RQ
Pin Number
|
Signal |
Type |
Description |
23
|
22
|
C0
|
Input/Output
|
Configurable function
|
22
|
21
|
C1
|
Input/Output
|
Configurable function
|
13
|
10
|
C2
|
Input/Output
|
Configurable function
|
14
|
11
|
C3
|
Input/Output
|
Configurable function
|
A number of D2XX driver commands are needed to use Asynchronous Bit Bang mode. The commands of interest are listed below:
D2XX Function
|
Description
|
FT_SetBitMode
|
Asynchronous Bit Bang mode is enabled using the FT_SetBitMode command. A value of 0x01 will enable it and a value of 0x00 will reset the device mode.
|
FT_SetBaudRate
|
The rate of data transfer can be controlled by using the FT_SetBaudRate command. The maximum Baud rate is 3MBaud, but to allow time for the data to be setup and held around the WR# strobe the Baud rate should be less than 1MBaud.
The clock for the Asynchronous Bit Bang mode is actually 16 times the Baud rate. A value of 9600 Baud would transfer the data at (9600x16) = 153600 bytes per second, or 1 every 6.5 mS. |
FT_Write
|
Data can be written to the device in Asynchronous Bit Bang mode using the FT_Write command. If multiple bytes are written to the device the values on the pins will change at the rate set by FT_SetBaudRate.
|
FT_GetBitMode
|
FT_GetBitMode returns the instantaneous value of the pins. A single byte will be returned containing the current values of the pins, both those which are inputs and those which are outputs.
|
FT_Read
|
FT_Read will return a buffer of values which have been sampled from the pins at the rate set by FT_SetBaudRate. If the read buffers have filled, data willl be lost. Each byte returned contains the values of the pins, both those which are inputs and those which are outputs.
|
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.