Remote-processing RPC-2350 Manuel d'utilisateur télécharger pdf (Page 35)

DIGITAL LINES CHAPTER 6

6-2

Figure 6-2 Inductive load protection

J3, port A is shared with the LCD character display port

J6. If you are using J6, then these 8 lines at J3 are not

available.

J3, port B is connected to a high current sink through

U20. See High current output later in this chapter. Two

lines are connected to the keypad port. They are active

only when scanning a 24 position keypad.

J3 port C is shared with the keypad port J5. If you are

using a keypad through J5, these 8 lines are not available

at J3.

Pull up resistors

Digital I/O lines at J2 and J3 are pulled up to + 5 volts

through a 10K resistor pack.

These pull ups makes interfacing to switches and "open

collector" TTL devices easy . See "Inter facing to

Switches and other devices" below.

High cu rrent ou tput at J3

Eight lines at J3 can be used as high current driver s.

These outputs switch loads to ground. Outputs are

controlled by Port B on the 82C55. Its address is 65.

Logic outputs from this port are inverted. That is, when

a 1 is written to the high cur rent por t, the output is

switched on and goes low.

The output driver chip, U 20, can be replaced with a DIP

shunt jumper so it is like the other lines at J3.

NOTE: Outputs at the high current lines are not

compatible with TT L logic levels and should

not be used to drive other logic devices.

Each of the high current outputs can sink 100 mA.at

50V.

Two lines from the high current port (Port B, 0 and 1)

are used when the keypad is scanning 24 keys. These

lines (at J3-8 and -10) may not be used for control

purposes.

WARNING:

External supplies using the high current outputs m ust

be tied to J3, pin 26 and NOT the power connector.

Failure to do so can produce a ground loop and

cause erratic operation.

The thermal time constant of U20 is very short, so the

number of outputs th at are on a t any one time should

include those that overlap even for a few milliseconds.

Incandescent lamps have a " cold" current of 11 times its

operating current. Lamps requiring more than 50 mA.

should not be used.

Protection diodes m ust be used with inductive loads.

Refer to figure 6-2.

Do not parallel outputs for higher drive. This could

result in damage since outputs do not share current

equally.

High current output at P2

The P2 terminal marked “SWPW R” is a 2 Am p, 50V

FET switch to ground. ON resistance is about 1 ohm.

It is intended to switch back light power for the LCD

graphics display. However, it can be used for any other

purpose.

The switch is controlled by software as follows:

OUT &E7,1 :’Turns on switch

OUT &E7,0 :’Turns off switch

The switch is turned OFF when only on a hardware reset

or watchdog timeout.

Use the circuit in Figure 6-2 when switching inductive

loads.

Interfacing to an opto-module rack

J2 and J3 I/O lines interface to an MPS-8, 16, or 24

position opto module rac k. L ines not going to an opto

module connect to a screw terminal on the MPS-XX

series boards. This feature allows you to connect

switches or other TTL type devices to the digital I/O

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Remote-processing RPC-2350 Manuel d'utilisateur Page 35

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