MKS 651D Series, Руководство пользователя, Страница: 123 / 162

Chapter Six: Remote Digital Logic Control General Information
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Chapter Six: Remote Digital Logic Control
General Information
Digital and analog control of the 651 unit is accomplished via the Interface connector located on
the rear panel. Refer to Table 8, for the Interface connector pinout.
Note Any RS-232 command takes priority over digital logic commands. For
example, a valve being held closed with a digital logic command can be
commanded to control to the level of set point A with the
D1 command
(refer to How To Activate a Set Point for more information).
Digital inputs and outputs are designed to interface with low power TTL and CMOS logic
families. They also include additional components to protect against damage from ESD or
transient voltages.
How To Select the Digital Input Functions
The Interface (I/O) board contains 16 type 74HC inputs . The specific function of each digital
input is listed in Table 17, page 112. To select an input function, pull the appropriate input pin
to a TTL low level (0 to 0.8 Volts) for a minimum of 50 milliseconds. If a higher priority
function has not already been selected, the requested function will be activated.
The TTL low signal is “level sensitive” meaning that once the signal is held low, the 651 unit
may take up to 50 milliseconds to recognize the command. The line must be held low
continuously for the 651 unit to use the selected parameters. Once the signal goes high, the
controller will default back to the state associated with the high signal within 50 milliseconds.
Each input consists of a single pole filter and pull-up resistor as shown in Figure 16.
When the input is brought high (+2.4 to +5 Volts), any lower priority functions that have been
selected will be activated. If no lower priority functions have been selected, the function most
recently requested remains in effect.
µ
Digital Ground
To input port
(74HC541)
I/O Connector
4.7k
0.01 FD
µ 0.01 FD
4.7k
+5 V
Figure 16: I/O Board Digital Input Circuitry