NSC800 datasheet(71/76 Pages) NSC

71 / 76 page

130 Data Acquisition System (Continued)

ing When in the power-save mode the system power re-

quirements are decreased by about 50% thus extending

battery life

Communication with the peripheral devices (MM58167 and

ADC0816) is accomplished through the IO ports of the

NSC810A and NSC831 The peripheral devices are not con-

nected to the bus of the NSC800 as they are not directly

compatible with a multiplexed bus structure Therefore ad-

ditional components would be required to place them on the

microprocessor bus Writing data into the MM58167 is per-

formed by first putting the desired data on Port A followed

by selecting the address of the internal register and applying

the chip select through the use of Port B A bit set and clear

operation is performed to emulate a pulse on the bit of Port

B connected to the WR input of the MM58167 For a read

operation the same sequence of operations is performed

except that Port A is set for the input mode of operation and

the RD line is pulsed Similar techniques are used to read

converted data from the AD converter When a conversion

is desired the CPU selects a channel and commands the

ADC0816 to start a conversion When the conversion is

complete the converter will produce an End-of-Conversion

signal which is connected to the RSTA interrupt input of the

NSC800

When operating the system shown consumes about 125

mw When in the power-save mode power consumption is

decreased to about 70 mw If as is likely the system is in

the power-save mode most of the time battery life can be

quite long depending on the amp-hour rating of the batteries

incorporated into the system For example if the battery

pack is rated at 5 amp-hours the system should be able to

operate for about 400-500 hours before a battery charge or

change is required

As shown in the schematic (refer to

Figure 20 ) analog input

IN0 is connected to the battery source In this way the CPU

can monitor its own power source and notify the host that it

needs a battery replacement or charge Since the battery

source shown is a stacked array of 7 NiCads producing

84V the converter input is connected in the middle so that

it can take a reading on two or three of the cells Since

NiCad batteries have a relatively constant voltage output

until very nearly discharged the CPU can sense that the

‘‘knee’’ of the discharge curve has been reached and notify

the host

Typical Timer Output Frequencies

Crystal Frequency

CPU Clock Output

Timer 0 Output

Timer 1 Output

2097152 MHz

1048576 MHz

262144 kHz

32768 kHz

divisor e 4

divisor e 8

3276800 MHz

1638400 MHz

327680 kHz

32768 kHz

divisor e 5

divisor e 10

4194304 MHz

2097152 MHz

262144 kHz

32768 kHz

divisor e 8

4915200 MHz

2457600 MHz

491520 kHz

32768 kHz

divisor e 5

divisor e 15

NSC800 Datasheet(PDF) 71 Page - National Semiconductor (TI)

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