Keithley 6487 Reference Manual

8-14 Limit Tests and Digital I/O Model 6487 Reference Manual
Source mode — logic control
The digital outputs can be used as logic inputs to active TTL, low-power TTL, or CMOS
inputs. For this mode of operation, the output lines can source up to 2mA.
`^rqflk Each output line can source up to 2mA. Exceeding 2mA may cause
damage to
the Model 6487 that is not covered by the warranty.
Figure 8-11 shows how to connect a logic device to one of the output lines. When the out-
put line is set HI, the transistor will turn off (transistor switch open) to provide a reliable
logic high output (>3.75V). When the output line is set LO, the transistor turns on (transis-
tor switch closed) to route current to digital ground. As a result, a low logic output (0V) is
provided at the output.
If the second input (B) of the NAND gate is connected to another output line of the port,
the output of the NAND gate will go to logic 0 when both digital outputs are set HI.
Figure 8-11
NAND gate control
Setting digital output lines
Digital output lines are set by selecting a decimal value (0 to 15) that corresponds to the
4-bit BCD pattern of the output. To determine the value, add up the decimal weight values
for the desired HI lines:
Output HI Line: Out 4 Out 3 Out 2 Out 1
Decimal Weight: 8 4 2 1
+5V
1kΩ
Pull Up
Resistor
Pin 9
Pin 1
Logic
Device
NAND
B
A
Model 6487

Keithley 6487 Specifications

General

Type	Picoammeter/Voltage Source
Current Measurement Range	20 fA to 20 mA
Interfaces	GPIB, RS-232
Voltage Burden	< 200 µV
Input Impedance	>10^14 Ω
Power	100 V / 120 V / 220 V / 240 V
Basic Current Measurement Accuracy	0.4%