Xycom XVME 590, Manual

Page: 62 / 102

XVME-500/590 Manual
February, 1988
3.4.1.3
Random Channel Selection
In the random-channel mode: A control byte written to the gain/channel register
- - which specifies a channel number and sets bit D5 to logic ‘0’ -- will auto-
matically start a conversion on the specified channel.
Procedure
1)
2)
Write a control byte to the status/control register that sets bit D5 to
logic ‘0’, and bit D6 to logic ‘1’.
Select the desired channel and initiate the conversion by writing the
channel number to bits D0 thru D4, and logic ‘0’ to bit D5 of the
gain/channel register.
Assuming that the corresponding Gain RAM was
properly initialized (programmed) after power-up, this action will initiate
a conversion with the correct gain on a specified channel. A conversion
may also be forced by using bit D7 of the status/control register.
3) The result of the conversion can be read from the A/D data registers
(base = 86H - 87H) in either the byte or word format. In the random-
channel mode, the data resulting from a conversion will remain in the
A/D registers until another conversion is initiated.
3.4.1.4
External Trigger Conversion Mode
To access the external-trigger mode, jumper J17 must be installed and jumper J21D
must be removed.
This allows the rising edge of a low-going, externally triggered
pulse (on pin 50 of JKl or pin P2C-25 on P2 of XVME-590) -- referenced to logic
ground (pin 49 of JKl or pin P2A-25 on P2 of XVME-590) -- to initiate a
conversion. Figure 3-6 shows the timing constraints.
3-18