5

Bit Bang Modes for the FT232R and FT245R

Copyright © 2006 Future Technology Devices International Ltd.

1.3

Synchronous Bit Bang Mode

Synchronous Bit Bang mode is the same as the FT2232 Synchronous Bit Bang mode. With

Synchronous Bit Bang mode, data will only be sent out if there is space in the device for data to be

read from the pins. This Synchronous Bit Bang mode will read the data bus pins first, before it

sends out the byte that has just been transmitted. 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:

· Pins start at 0xFF

· Send 0x55, 0xAA

· Pins go to 0x55 and then to 0xAA

· Data read = 0xFF, 0x55

· 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

The timing for Synchronous Bit bang is described in this diagram and the table below:

Time

Description

t1

Current pin state is read

t2

RD# is set inactive

t3

RD# is set active again, and any pins that are

output will change to the new data.

t4

Clock state for data setup

t5

WR# goes active

t6

WR# goes inactive

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.