Agilent Technologies 4294A, Руководство по программированию

Страница: 123 / 518

Chapter 9 123
Communication with External Equipment (Using the I/O Ports)
Using the I/O Ports
1. Ch
apter
T
itle
2
. Cha
p
te
r T
itle
3
. Chap
te
r T
itle
9.
Communication w
ith
5. Chap
te
r T
itle
Exer
nal Equ
ipme
n
t
(U
s
ing
th
e I/
O Por
ts
)
Input/output port
The 24-bit I/O port of the 4294A consists of 2 sets of output ports and 2 sets of
bi-directional ports as shown below.
• Output port
Port A: 8-bit width (LSB: A0, MSB: A7)
Port B: 8-bit width (LSB: B0, MSB: B7)
The signals provide TTL level and latched when used as output.
• Bi-directional port
Port C: 4-bit width (LSB: C0, MSB: C3)
Port D: 4-bit width (LSB: D0, MSB: D3)
The signals provide TTL level and latched when used as output. To select the input/output
direction, use the GPIB command. At power-on, both port C and port D are set to input.
You can combine some of the above 4 ports to use them as 4 kinds of ports as shown below.
• Bi-directional port
Port E: 8-bit width (port C + port D, LSB: C0, MSB: D3)
• Output port
Port F: 16-bit width (port A + port B, LSB: A0, MSB: B7)
Port G: 20-bit width (port A + port B + port C, LSB: A0, MSB: C3)
Port H: 24-bit width (port A + port B + port C + port D, LSB: A0, MSB: D3)
Control signal lines
The 24-bit I/O port has 9 kinds of output signal lines and 1 kind of input signal line. The
signals except for the power line provide TTL level. Each signal is described below.
Port C status output, port D status output
Go LOW when Port C and port D are both set to input ports; HIGH when set to output
ports. These output signals notify external equipment of the input/output settings of port C
and port D.
Write strobe output for output ports
When data is outputted to one of the output ports, this write strobe output falls to indicate
that data is outputted the I/O output port for external equipment. The pulse width is 10
μ
s
(typical). Figure 9-3 shows the relationship between the write strobe output and data
output.
Figure 9-3 Relationship between the write strobe signal and data output
INPUT1 input