USB232 Converter User Guide
1-1
1. Introduction
RS232 is still commonly used by industrial equipment manufacturers. Its purpose is usually for setup,
commissioning, diagnostics, and firmware upgrades to individual devices like PLCs, motion controllers,
drives, sensors, etc. Usually, the systems engineer or technician is working out on the factory floor with a
laptop PC. The problem is that it is getting harder to find a new laptop with legacy COMM ports.
The usual solution is to purchase a USB to RS232 converter in the form of a dongle. Implementations to
date using the FTDI or Prolific chip have not been very successful. The failure modes have been to either
stop working, or to crash the operating system. Some laptops still available with COMM ports go through a
USB layer internally and suffer from the same problems.
The Exar USB UART hardware and software is by far the best solution to date. The Exar evaluation board
has been tested by a major motion control distributor and found to be compatible with almost all existing
and legacy products, as well as other vendor OEM products. The USB232 converter design uses the Exar
evaluation board as a reference design. The optimized drivers supplied by Exar will be used. A block
diagram is shown below.
Internal
48MHz
Oscillator
USB Device
Interface
128-byte
TX FIFO
384-byte
RX FIFO
MODEM I/O
Internal
Status and
Control
Registers
Baud
Rate
Generator
UART
TX
RX
RTS
CTS
DTR
DSR
CD
RI
XR21V1410
VBUS
DM
DP
GND
USB B-Type
Connector
Soft
Start
+3.3V
Regulator
RS232
Interface
RS232-TX
RS232-RX
RS232-RTS
CTS
DTR
DSR
CD
RI
RS232-
RS232-
RS232-
RS232-
RS232-
DB9 Male
Connector
9
1
6
4
8
7
3
2
Figure 1-USB-232 Block Diagram
