
7
LTC1387
BLOCK DIAGRAM
W
RS232 MODE
WITHOUT LOOPBACK
ON
13
RA
C2
C1
RB
DY
DZ
B
A
VDD
VCC
19
20
1
4
2
3
6
7
8
18
16
15
14
Y
Z
5
17
GND
DXEN
485/232
10
9
LTC1387 BD
RXEN
12
11
VEE
RS232 MODE
WITH LOOPBACK
ON
13
RA
C2
C1
RB
DY
DZ
VDD
VCC
19
20
1
2
3
6
7
8
18
16
15
14
Y
Z
17
GND
DXEN*
485/232
10
9
RXEN*
12
11
VEE
RS485 MODE
WITHOUT LOOPBACK
ON
13
RA
C2
C1
RB
DY
SLEW
B
A
VDD
VCC
19
20
1
4
2
3
6
7
8
18
16
15
14
Y
Z
5
17
GND
DXEN
485/232*
10
9
RXEN
12
11
VEE
RS485 MODE
WITH LOOPBACK
ON
13
RA
C2
C1
RB
DY
SLEW
VDD
VCC
19
20
1
2
3
6
7
8
18
16
15
14
Y
Z
17
GND
DXEN*
485/232*
10
9
RXEN*
12
11
VEE
*485/232, DXEN, RXEN = VCC
TEST CIRCUITS
Figure 2. RS485 Driver/Receiver
Timing Test Circuit
Figure 1. RS485 Driver
Test Load
R
VOD
Z
Y
LTC1387 F01
VOC
RL
CL
LTC1387 F02
Z
Y
CL
B
R
A
15pF
D
SLEW
485 = 3V, DXEN = 3V, RXEN = 3V
Figure 3. RS485 Driver Output
Enable/Disable Timing Test Load
DR OUT
CL
500
S2
LTC1387 F03
VCC
S1
Figure 4. RS232 Driver
Timing Test Circuit
Figure 6. Receiver Output
Enable/Disable Timing Test Load
RECEIVER
OUT
CL
1k
S2
LTC1387 F06
VCC
S1
Figure 5. RS232 Receiver
Timing Test Circuit
LTC1387 F05
15pF
Y, Z
D
R
A, B
232 = 0V, DXEN = 3V, RXEN = 3V
RL
LTC1387 F04
Y, Z
D
CL
232 = 0V, DXEN = 3V