4
AN1248.1
May 30, 2006
Driver Tests
There are no driver loads on this board, so if loading is
desired a differential load resistor, and/or differential load
capacitor may be added at position “R7”. Alternatively, single
ended loads (Y or Z to GND) may be added at positions “C4”
and “C2”.
Ensure that the “DZ1/DE1 (DY)”
(14)
jumper is in the “LOW”
position to engage the 50
Ω
term resistor, connect the
generator to the “DZ1/DE1 (DY)” BNC, and set the swing for
0 to 3V. Monitoring test points “TP18” (input), and “TP5” and
“TP2” (Y and Z outputs respectively) with a scope allows the
Tx prop delays, skews, and transition times to be measured.
To view the differential waveform, use the scope’s math
function to generate “Z-Y”.
To measure the Tx output enable and disable times, start
with the previous jumper configuration and move the
“DEN”
(8)
jumper to the “LOW” position to engage its 50
Ω
term resistor. Connect the generator to the “NC (DEN)” BNC,
and set the swing for 0 to 3V. Monitoring test points “TP9”
(input), and “TP5” and “TP2” (Y and Z outputs respectively)
with a scope allows the enable and disable times to be
measured. Note that some form of termination resistor must
be used to pull the disabled outputs to a known state; a
differential termination resistor at “R7” is the easiest
approach.
Evaluating Driver and Receiver Combined Performance
Performance through a cascaded Tx and Rx can easily be
evaluated, utilizing the external loopback function, by
installing jumpers “A1/Y1_LB
(5)
and “B1/Z1_LB
(6)
. In this
configuration, the Tx output lines connect to the
corresponding Rx input lines, so the data driven on the Tx
input (DY) appears at the Rx output (RA).
Installing resistors R7 and R9 allows evaluation of the
performance with the Tx driving a double terminated load.
Interconnecting Driver and Receiver with a Cable
To evaluate the performance of the Tx and Rx
interconnected by a cable, start with the default
configuration, connect single wire of a twisted pair between
test points “TP2” and “TP1”, and connect the other wire in
the pair between “TP5” and “TP6”. Ensure that the
“DZ1/DE1 (DY)”
(14)
jumper is in the “LOW” position to
engage the 50
Ω
term resistor, connect the generator to the
“DZ1/DE1 (DY)” BNC, and set the swing for 0 to 3V.
Monitoring test points “TP18” (input), and test point
“RB1(RA)” illustrates the overall input to output performance.
Installing resistors R7 and R9 allows evaluation of the
performance with the Tx driving a double terminated cable.
Switching to RS-232 Mode
To set the board for RS-232 evaluation, start with the
jumpers in the “default configuration”, and move jumper
“A2 (485/232)”
(7)
to the “LOW” position. If RS-485
termination resistors (“R7” or “R9”) were added, ensure that
they have been removed. Note that the RS-232 data rate is
fixed at 500kbps, so the “SPB”
(9)
jumper has no affect
(connect it high to minimize SHDN I
CC
), and that the
“SLEW” pin becomes the second driver input, DZ. Figure 1
illustrates the 41387 configuration in this mode.
Basic RS-232 DC Evaluation
General Observations
Note that V+ and V- now pump up to approxi6V and
-7V, respectively, and the charge pump operation increases
I
CC
to 3.8mA. Also note that RS-232 drivers and receivers
are inverting by definition.
Before starting, ensure that resistors R7 and R9 are
removed, if they have been previously installed.
Receiver Tests
In the default configuration of Figure 1, RB (measure at the
“RA1 (RB)” test point to the left of jumper
(14)
) and RA
(measure at the “RB1(RA)” test point to the right of
TABLE 1. JUMPER SETTINGS FOR Tx SPEED SELECTION
DATA RATE
J-(DZ/SLEW)
(13)
J-SPB
(9)
115kbps
“LOW”
“LOW”
460kbps
“LOW”
“VH”
20Mbps
“VH”
“LOW” or “VH”
Y1
Z1
D
Y
D
Z
0.1
μ
F
+
0.1
μ
F
+
0.1
μ
F
28
27
4
5
37
38
1
19
V+
V-
C1+
C1-
C2+
C2-
+
0.1
μ
F
36
35
R
A
A1
2
5k
Ω
R
B
B1
3
29
5k
Ω
C
1
C
2
+ C
3
C
4
RXEN
17
GND
+5V
+
0.1
μ
F
15, 16
485 / 232
ON
11
21
V
H
V
H
DEN
12
V
H
30
R
R
D
D
34
V
CC
31
V
L
RXEN
20
V
H
FIGURE 1. DEFAULT RS-232 CONFIGURATION
VHIGH (V
H
)
(17)
(16)
V
H
Application Note 1248
