MC33794 Просмотр технического описания (PDF) - Motorola => Freescale

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MC33794

Electric Field Imaging Device

Motorola => Freescale 

HSOP PIN FUNCTION DESCRIPTION (continued)

Pin

Pin Name

Formal Name

21

ISO-9141

ISO-9141 Bus

22

LAMP_OUT

Lamp Driver

23

RST

Reset

24

WD_IN

Watchdog Input

25

LAMP_GND

26

LAMP_CTRL

28

LAMP_SENSE

Lamp Ground

Lamp Control

Lamp Sense

29

LAMP_MON

Lamp Monitor

30

DIS_SHIELD

Shield Driver Disable

34–31

35

A, B, C, D

SIGNAL

Selector Inputs

Undetected Signal

36

LEVEL

Detected Level

37

PWR_MON

Power Monitor

38

LP_CAP

Low-Pass Filter Capacitor

Definition

This pin connects to the ISO-9141 bus. It provides the drive and detects signaling on

the bus and translates it from the bus level to logic levels for the MCU.

This is an active low output capable of sinking current of a typical indicator lamp. One

end of the lamp should be connected to a positive supply (for example, battery

voltage) and the other side to this pin. The current is limited to prevent damage to the

IC in the case of a short or surge during lamp turn-on or burn-out.

This output is intended to generate the reset function of a typical MCU. It has a delay

for power-on reset, level detectors to force a reset when VCC is out-of-range high or

low, and a watchdog timer that will force a reset if WD_IN is not asserted at regular

intervals. Timing is derived from the oscillator and will change with changes in the

resistor attached to R_OSC.

This pin must be asserted and deasserted at regular interval in order to prevent RST

from being asserted. By having the MCU program perform this operation more often

the allowed time, a check that the MCU is running and executing its program is

assured. If this doesn’t occur, the MCU will be reset. If the watchdog function is not

desired, this pin may be connected to CLK to prevent a reset from being issued.

This is the ground for the current from the lamp. The current into LAMP_OUT flows

out through this pin.

This signal is used to control the lamp driver. A high logic level turns on the lamp.

This pin is normally connected to the LAMP_OUT pin. The voltage at this pin is

reduced and sent to LAMP_MON so the voltage at the lamp pin is brought into the

range of the analog-to-digital converter (ADC) in the MCU.

This pin is connected through a voltage divider to the LAMP_SENSE pin. The voltage

divider scales the voltage at this pin so that battery voltage present when the lamp is

off is scaled to the range of the MCU ADC. With the lamp off, this pin will be very close

to battery voltage if the lamp is not burned out and the pin is not shorted to ground.

This is useful as a lamp check.

This pin is used to turn off the shield signal. The purpose of doing this is to be able to

detect that the shield signal is not working or the connection to the coax shields is

broken. If either of these conditions exists, there will be little or no change in the

capacitance measured when the DIS_SHIELD is asserted. If the SHIELD output is

working and properly connected, the capacitance of the coax will not be cancelled

when this pin is asserted and the measured capacitance will appear to change by

approximately the capacitance between the center conductor and the shield in the

coax.

These input pins control which electrode or reference is active. Selection values are

shown in Table 1, Electrode Selection, page 14.

This is the undetected signal being applied to the detector. It has a DC level with the

low radio frequency signal superimposed on it. Care must be taken to minimize DC

loading of this signal. A shift of DC will change the center point of the signal and

adversely affect the detection of the signal.

This is the detected, amplified, and offset representation of the signal voltage on the

selected electrode. Filtering of the rectified signal is performed by a capacitor

attached to LP_CAP.

This is connected through a voltage divider to VPWR. It allows reduction of the voltage

so it will fall within the range of the ADC on the MCU.

A capacitor on this pin forms a low pass filter with the internal series resistance from

the detector to this pin. This pin can be used to determine the detected level before

amplification or offset is applied. A 10 nF capacitor connected to this pin will smooth

the rectified signal. More capacitance will increase the response time unnecessarily.

33794

4

MOTOROLA ANALOG INTEGRATED CIRCUIT DEVICE DATA

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