Serial Port Complete - Latest Microcontroller projects

Using Special-function USB Controllers

when the CPU can read a byte from the FT245R, and the CPU strobes RD# to

read the byte. In the other direction, the TXE# output goes low when the CPU

can write a byte to the FT245R, and the CPU strobes WR# to write the byte

into the FT245R’s buffer. An external CPU can use a data bus or any spare port

pins to access the FT245R’s parallel port. Parameters such as bit rate and parity

don’t apply to this chip.

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FTDI’s controllers are available only in surface-mount packages. For prototyp-

ing, FTDI and other vendors offer a variety of converters and development

boards. FTDI’s UM232R and UM245R modules (Figure 15-3) each consist of

a circuit board with a controller chip, USB connector, and related circuits

mounted on a 24-pin dual in-line package (DIP).

For interfacing a PC to a microcontroller’s serial port, FTDI’s TTL-232R serial

converter cable provides a quick solution. Inside the cable’s USB connector is

an FT232R circuit. The other end of the cable has a 6-pin socket header that

Figure 15-3: For easy prototyping with FTDIs’ controllers, use the UM232R and

UM245R modules.