FT232H datasheet(34/65 Pages) FTDI

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Document No.: FT_000288

FT232H SINGLE CHANNEL HI-SPEED USB TO MULTIPURPOSE UART/FIFO IC

Datasheet Version 1.81

Clearance No.: FTDI #199

4.7 Synchronous and Asynchronous Bit-Bang Interface Mode

The FT232H can be configured as a bit-bang interface. There are two types of bit-bang modes:

synchronous and asynchronous.

See application note AN2232-02 Bit Mode Functions for the FT232 for more details and examples of

using both Synchronous and Asynchronous bit-bang modes.

4.7.1

Asynchronous Bit-Bang Mode

Asynchronous Bit-Bang mode is the same as BM-style Bit-Bang mode, except that the internal RD# and

WR# strobes (RDSTB# and WRSTB#) are now brought out of the device to allow external logic to be

clocked by accesses to the bit-bang IO bus.

Any data written to the device in the normal manner will be self clocked onto the data pins (those which

have been configured as outputs). Each pin can be independently set as an input or an output. The rate

that the data is clocked out at is controlled by the baud rate generator.

New data must be written, and the baud rate clock should tick to change the data. If no new data is

written to the chip, the pins configured for output will hold the last value written.

Asynchronous Bit-Bang mode is enabled using the FT_SetBitMode D2xx driver command with a hex value

of 0x01.

4.7.2

Synchronous Bit-Bang Mode

The synchronous Bit-Bang mode will only update the output parallel port pins whenever data is sent from

the USB interface to the parallel interface. When this is done, the WRSTB# will activate to indicate that

the data has been read from the USB Rx FIFO buffer and written out on the pins. Data can only be

received from the parallel pins (to the USB Tx FIFO interface) after the parallel interface has been written

to.

With Synchronous Bit-Bang mode data will only be sent out by the FT232H if there is space in the

FT232H USB TXFIFO for data to be read from the parallel interface pins. This Synchronous Bit-Bang mode

will read the data bus parallel I/O pins first, before it transmits data from the USB RxFIFO. It is therefore

1 byte behind the output, and so to read the inputs for the byte that you have just sent, another byte

must be sent.

For example:

Figure 1.

Pins start at 0xFF

Send 0x55, 0xAA

Pins go to 0x55 and then to 0xAA

Data read = 0xFF,0x55

(2) Pins start at 0xFF

Send 0x55, 0xAA, 0xAA

(repeat the last byte sent)

Pins go to 0x55 and then to 0xAA

Data read = 0xFF, 0x55, 0xAA

Synchronous Bit-Bang Mode differs from Asynchronous Bit-Bang mode in that the device parallel output

is only read when the parallel output is written to by the USB interface. This makes it easier for the

controlling program to measure the response to a USB output stimulus as the data returned to the USB

interface is synchronous to the output data.

Synchronous Bit-Bang mode is enabled using Set Bit Bang Mode driver command with a hex value of

0x04.

An example of the synchronous bit-bang mode timing is shown in Figure 4.12

FT232H Datasheet(PDF) 34 Page - Future Technology Devices International Ltd.

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