26-Aug-10 USB-232 HW143-19 www.firmwarefactory.com RS485 Converter RS485 is a bus configuration which allows " />
參數(shù)資料
型號: USB-232-DIL
廠商: Flexipanel
文件頁數(shù): 9/11頁
文件大?。?/td> 0K
描述: IC USB ASYNC SRL UART 28-DIL
標準包裝: 25
應用: USB
接口: I²C,SPI
電源電壓: 3.3 V ~ 5 V
封裝/外殼: 28-DIP
供應商設備封裝: 28-DIL
包裝: 散裝
安裝類型: 通孔
產(chǎn)品目錄頁面: 659 (CN2011-ZH PDF)
其它名稱: 658-1032-5
p7 of 11
26-Aug-10
USB-232
HW143-19
www.firmwarefactory.com
RS485 Converter
RS485 is a bus configuration which allows each device
to broadcast data to all other devices on the bus via just
two differential lines A and B. Only one device may
transmit at a time.
An RS485 converter such as a
MAX481 is used to create the A and B signals, as
shown in figure 7.
Both ends of the bus must be
terminated by 120Ω resistors (i.e. two resistors for the
entire bus). These are not shown in figure 8, but they
are in figure 9.
R
es
et
#
P
G
D
V
dd
V
ss
TEAclipper
connector 1
5
OSC1
OSC2
D+
Vusb
USB-232
USB
C2
C3
X1
2
3
4
Vdd
Vss
Vdd
P
G
C
1
2
3
4
Vss
D-
Vss
C1
C6
C7
V
ss
C8
DCD#
DSR#
Suspend
RI#
AllSysGo#
Vdd
Vss
Reset#
Vss
R1x
PB1x
Send
One pushbutton
circuit for each input
(Active low shown)
DTR#
Buff Empty
Tx Ind
Rx Ind
Vdd
R2x
One LED circuit
for each output
(Active low shown)
T
xD
#
R
xD
#
T
xE
n
S
us
pe
nd
#
MAX481
Vdd
Vss
Vcc
Gnd
D
I
D
O
R
E
#
A
B
D
E
R
S
48
5
-
B
R
S
48
5
-
A
Fig 8
RS422 Converter
RS422 is similar to RS485 except only two devices
communicate with each other, and use a pair of
differential lines. In this ‘full-duplex’ setup both devices
may transmit at the same time if required. Since the
receiver inputs A and B in figure 9 will be, by definition,
at the end of the ‘bus’, a 120Ω terminating resistor is
required as shown.
Figure 9 does not provide flow
control lines RTS and CTS. If they are required, a
second MAX491 can be added.
R
es
e
t#
P
G
D
V
dd
V
ss
TEAclipper
connector 1
5
OSC1
OSC2
D+
Vusb
USB-232
USB
C2
C3
X1
2
3
4
Vdd
Vss
Vdd
P
G
C
1
2
3
4
Vss
D-
Vss
C1
C6
C7
V
ss
C8
DCD#
DSR#
Suspend
RI#
AllSysGo#
Vdd
Vss
Reset#
Vss
R1x
PB1x
Send
One pushbutton
circuit for each input
(Active low shown)
DTR#
Buff Empty
Tx Ind
Rx Ind
Vdd
R2x
One LED circuit
for each output
(Active low shown)
T
xD
#
R
xD
#
T
xE
n
S
us
pe
nd
#
MAX491
Vdd
Vss
Vcc
Gnd
D
I
D
O
R
E
#
X
Y
D
E
R
S
42
2
-
B
R
S
42
2
-
A
B
R
S
42
2
-
X
R
S
42
2
-
Y
R7
Connect X & Y
at one end to
A & B at the other
Fig 9.
Power considerations
Initially, the device will request the full power it is
configured for. If it is not granted this power level within
three seconds, it performs a soft detach and requests a
maximum of 100mA. This allows devices to operate in a
low power mode when connected to an unpowered hub.
This reduced power mode is indicated by the Low Pwr
Indication pin.
In RS232, RS485 and RS422 systems, independently
powered devices may float at different voltages; in
addition exceptional voltages can be introduced from
other sources along the signal lines. Consider adding
current limiting resistors or opto-isolators if this is a
possibility. The shield on the RS232 connector should
be left unconnected.
If the device is electromagnetically noisy, a ferrite bead
is recommended on the USB Vdd supply in order to
suppress any transmission of noise to the rest of the
USB network. 100nF smoothing capacitors should be
provided on all independently switched power rail to
avoid momentary brown-out conditions.
When designing self powered circuits, ensure power can
never be fed into the Vdd USB line.
Design note
AN1149 from Microchip Technology, in the development
kit, discusses designs for recharging batteries using
USB bus power.
USB Connectors
Common USB connector and cable configurations are
shown in figure 10 and table 5.
The shield on the
connector should be left unconnected. The ID pin on
the mini connector permits the distinction of A and B
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