68HC705SP7 datasheet(134/230 Pages) FREESCALE

134 / 230 page

Analog Subsystem

General Release Specification

MC68HC705JJ7/MC68HC705JP7 — Rev. 3.0

Analog Subsystem

8.8.2 Voltage Comparator 2

Voltage comparator 2 can be used as a simple comparator if its charge

current source and discharge device are disabled by clearing the ISEN

bit in the ACR. If the ISEN bit is set, the internal ramp discharge device

connected to PB0/AN0 may become active and try to pull down any

voltage source that may be connected to that pin. Also, since voltage

comparator 2 is always connected to two of the port B I/O pins, these

pins should be configured as inputs and have their software

programmable pulldowns disabled.

8.9 Current Source Features

The internal current source connected to the PB0/AN0 pin supplies

about 100

µA of current when the discharge device is disabled and the

current source is active. Therefore, this current source can be used in an

application if the ISEN enable bit is set to power up the current source

and by setting the A/D conversion method to manual mode 0 (ATD1 and

ATD2 cleared) and the charge current enabled (CHG set).

8.10 Internal Temperature Sensing Diode Features

An internal diode is forward biased to VSS and will have its voltage

change approximately 2 mV for each degree centigrade rise in the

temperature of the device. This temperature sensing diode is powered

up from a current source only during the time that the diode is selected.

When on, this current source adds about 30

µA to the I

DD current.

The temperature sensing diode can be selected by setting both the

HOLD and DHOLD bits in the AMUX register (see 8.3 Analog Multiplex

8.11 Sample and Hold

When using the internal sample capacitor to capture a voltage for later

conversion, the HOLD or DHOLD bit must be cleared first before

changing any channel selection. If both the HOLD (or DHOLD) bit and

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

68HC705SP7 датащи(PDF) 134 Page - Freescale Semiconductor, Inc