Motorola Axiom CMD11E1 Betriebsanweisung PDF herunterladen (Seite 96)

96 CHAPTER 9. ANALOG TO DIGITAL CONVERSION

this to 1 if you want scanning; or else, set it to zero. Bit #4 is the MULT bit. Set

this to 1 if you want multiplexing; or else, set it to zero. Bits #3-#0 specify which

PORT E pin you want to measure. In the multiplexed mode, you can specify any

of the four pins that are part of the multiplexed group.

9.5.3 Making sure you have valid data

Once you have initiated the conversion, you have to make sure you that you have

valid data. HC11 will turn on bit #7 of ADCTL once all four conversions are

complete. It is your responsibility to check this bit before reading the converted

values.

9.6 A trial dry run

We will ﬁrst do some analog to digital conversion without writing any programs.

1. Make the appropriate electrical connections. Make sure that you connect

PE7 to PE3, VRL to ground and 5V.

2. First turn on the convertor by storing $80 to location $1039. You do this

with the memory modify command: MM 1039 and entering the value 80.

3. Since it is going to take lot more than 100 microseconds for you to type

anything, there is no need for any waiting for the A/D to warm up. Now we

will conﬁgure the A/D to be in non-multiplexed, scan mode to measure PE3.

We do this by entering the bit pattern 00100011/ in location $1030. The

hexadecimal representation for the bit pattern is $23, and we need this for

memory modify command. Use the command MM 1030 and enter the value

23.

4. Adjust the input voltage so that it is one volt. use the command

md 1030 1030

and write down the ﬁrst ﬁve numbers. Note that the contents of location

$1030 is A3 and not 23. This because HC11 will turn the 7th bit at location

$1030 when the conversion is completed. The next four values should be

approximately 255/5 or 51 in decimal or 33 in hex. Verify that the next

four values are approximately 33.

5. Change the input voltage. Do a memory dump to see what the converted

values are. Since we conﬁgured the analog to digital convertor to be in the

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Motorola Axiom CMD11E1 Betriebsanweisung Seite 96