Document Number: 001-76294 Rev. *F Page 10 of 21
Application Diagram
USB to RS-232 Converter
In this example the procedure of using the CY7C64225 as a USB
to RS-232 converter is illustrated. In this application, a TTL to
RS232 Level Converter IC is used on the serial UART interface
of the CY7C74225 to convert the TTL levels of the CY7C64225
to RS-232 levels. RS-232 follows bipolar signaling i.e. the output
signal toggles between negative and positive polarity. In RS-232,
logic 1 is called Mark and is a –3 V input and logic 0 is called
Space and is a +3 V input. The output voltage level of RS-232 is
+/-5 V to +/-15 V. So there is not only an inversion in polarity but
also voltage level translation between the CY7C64225 UART
interface and RS-232 signaling. So, RS-232 line driver/receiver
is used for providing the necessary polarity inversion and level
translation.
The connection between CY7C64225 and the RS-232 line
driver/receiver is simple. The input lines (DSR, CTS and RX) of
the UART interface should be connected to the logic outputs of
the RS-232 line driver/receiver chip. The output lines (DTR, RTS
and TX) of the UART interface should be connected to the logic
inputs of the RS-232 line driver/receiver chip. The inverted,
level-translated UART output will be sent through the line driver
pins of the RS-232.
Figure 6. USB to RS-232 Converter Configuration
CY7C64225
1k
0.01uF
VDD
WAKEUP
1k
24
24
RESET
VDD
VDD
Rx_LED
VCFG
Tx_LED
SUSPEND
TxD
RxD
RTS
CTS
DTR
DSR
LEVEL
TRANSLATOR
Rx_1
Tx_1
CTS_1
RTS_1
DSR_1
DTR_1
SW2
GND
GND
VDD
VDD
VBUS
D+
D-
D+
D-
VBUS
GND
VDD
560
560
560
Tx_1
Rx_1
RTS_1
CTS_1
DTR_1
DSR_1
DB9 MALE
CONNECTOR
NO CONNECT
