DS232B Version 1.8

© Future Technology Devices Intl. Ltd. 2005

Page 17 of 25

FT232BM USB UART ( USB - Serial) I.C.

7.4 UART Interface Configuration

Figure 9

USB <=> RS232 Converter Configuration

12

14

2

7

8

4

6

1

9

VCC

SP213EHCA

T1In

T1Out

T2Out

T3Out

T4Out

R1In

T2In

T3In

T4In

R2In

R3In

R4In

R5In

EN

R1Out

R2Out

R3Out

R4Out

R5Out

SHDN#

25

7

22

20

8

6

5

26

19

21

11

2

23

1

9

3

4

27

16

28

VCC

C1+

C1-

C2+

C2-

V

C

C

V-

V+

15

16

10

11

3

13

17

G

N

D

VCC

0.1uF

0.1uF

0.1uF

0.1uF

0.1uF

5

FT232BM

PWREN#

SLEEP#

TXD

RXD

RTS#

CTS#

DTR#

DSR#

DCD#

RI#

10

TXDEN

25

24

23

22

15

21

20

19

18

16

DB9-M

TXD

RXD

RTS

DTR

CTS

DSR

DCD

RI

GND

Figure 9 illustrates how to connect the UART interface of the FT232BM to a TTL – RS232 Level Converter I.C. to

make a USB <=> RS232 converter using the popular “213” series of TTL to RS232 level converters. These devices

have 4 transmitters and 5 receivers in a 28 LD SSOP package and feature an in-built voltage converter to convert the

5v (nominal) VCC to the +/- 9 volts required by RS232. An important feature of these devices is the SHDN# pin which

can power down the device to a low quiescent current during USB suspend mode

The device used in the example is a Sipex SP213EHCA which is capable of RS232 communication at up to 500K

baud. If a lower baud rate is acceptable, then several pin compatible alternatives are available such as Sipex

SP213ECA , Maxim MAX213CAI and Analog Devices ADM213E which are good for communication at up to 115,200

baud. If a higher baud rate is desired, use a Maxim MAX3245CAI part which is capable of RS232 communication at

rates of up to 1M baud. The MAX3245 is not pin compatible with the 213 series devices, also its SHDN pin is active

high so connect this to PWREN# instead of SLEEP#.