Sensory Science 7405 - Manual (Page 4)

Sensoray Model 7405 Instruction Manual — Page 4
Programming Model
The Model 7405 board occupies two contiguous I/O ports in
the STDbus I/O space. Both ports may be written to, and the
base port has a read function as well.
Analog output data and channel number is written to the A
and B registers, while the status register is used by the host
processor for handshake control.
Note that the status register and A register share the same I/O
port address. This is possible because the status register is
read only while the A register is write only.
Status Register
The status register provides the host with a means for
monitoring Model 7405 handshake status. When the host
reads from the status port, a byte with the following form is
returned:
The status register contains two BUSY bits that are used to
handshake data onto the Model 7405 board. When both bits
are reset to logic 0, the board is ready to accept new data.
The remaining six bits are not used and should be ignored.
Prior to writing new data to the board, the host must read and
test the two BUSY bits. The host should write data to the
board only when both BUSY bits contain logic 0.
Although this handshake rule is simple, failure to observe it
will most likely result in communication errors.
Data Registers
Analog channel data may be written into the A and B
registers after ensuring that the status register handshake bits
are both reset to logic 0.
First the low data byte is written into the A register. Then
the B register is loaded with the high data nibble and channel
number.
Data Format
The analog channel data format is a function of the selected
output mode. Voltage mode employs a format different from
that of current mode. This table illustrates the relationship
between channel data value and signal output:
Connections
All output loads are connected to the Model 7405 through
40-pin flat cable connector P1. Optionally, loads may be
connected to the Model 7405TB screw termination board,
which in turn connects to P1 by means of flat ribbon cable.
Each channel has four dedicated pins on connector P1. Two
of the pins are used only in the voltage output mode, and the
other two only in current output mode. In addition, ground is
supplied on connector P1 pin 38 for use as a cable shield.
A channel circuit may be wired in one of two ways,
depending on the selected output mode (voltage versus
current). The following table specifies the proper connector
P1 pins to be used:
I/O
Address
Function
Read Write
Base Address + 0 Status Register A Register
Base Address + 1 (not used) B Register
BUSY BUSY
Not Used
Channel can be written to
D7 D6 D5 D4 D3 D2 D1 D0
when these are both zero
X X X X X X
Data Value
(Hexadecimal)
Voltage Mode
Output (V)
Current Mode
Output (mA)
000 -10.000 4.0000
001 -9.9951 4.0039
002 -9.9902 4.0078
...
7FF -0.0049 11.996
800 0.0000 12.000
801 +0.0049 12.004
...
FFE +9.9902 19.996
FFF +9.9951 20.000
D7 D6 D5 D4 D3 D2 D1 D0
B Register A Register
0
Analog Output Data Channel
D7 D6 D5 D4 D3 D2 D1 D0