ANALOG-TO-DIGITAL (A/D) CONVERTER

12.4.4 Programming the A/D Command Register

The A/D command register controls the operating mode, the analog input channel, and the conversion trigger.

AD_COMMAND	Address:	1E74H
	Reset State:	00H

The A/D command (AD_COMMAND) register selects the A/D channel number to be converted, controls whether the A/D converter starts immediately or with an EPA command, initiates automatic scan on selected A/D channel inputs, and selects the conversion mode.

7

0

SCAN

M1

M0

GO

ACH3

ACH2

ACH1

ACH0

Bit

Bit

Function

Number

Mnemonic

7

SCAN

A/D Scan

This bit enables and disables automatic scanning.

0

= disable scan

1

= enable scan

6:5

M1:0

A/D Mode†

These bits determine the A/D mode.

M1 M0

Mode

0

0

10-bit conversion

0

1

8-bit conversion

1

0

threshold detect low

1

1

threshold detect high

4

GO

A/D Conversion Trigger††

Writing this bit arms the A/D converter. The value that you write to it

determines at what point a conversion is to start.

0

= EPA initiates conversion

1

= start immediately

3:0

ACH3:0

A/D Channel Selection

Write the A/D conversion channel number to these bits. The 83C196EA

has 16 A/D channel inputs, numbered 0–15.

†While a threshold-detection mode is selected for an analog input pin, no other conversion can be started. If another value is loaded into AD_COMMAND, the threshold-detection mode is disabled and the new command is executed.

††It is the act of writing to the GO bit, rather than its value, that starts a conversion. Even if the GO bit has the desired value, you must set it again to start a conversion immediately or clear it again to arm it for an EPA-initiated conversion. The GO bit must be set to 0 for A/D SCAN to work.

Figure 12-5. A/D Command (AD_COMMAND) Register

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8XC196EA USER’S MANUAL

12.4.5 Programming the A/D Scan Register

The A/D can operate in a number of conversion modes. On the 8XC196EA, the A/D can operate in an automatic scan mode. In automatic scan mode, each channel is sampled automatically and the conversion result is loaded into the corresponding result register, AD_RESULTx, and AD_RESULT. The AD_SCAN register (Figure 12-6) allows you to include or exclude individual channels from the scan sequence. The scan sequence begins from the least-significant channel number and continues to the most-significant channel number.

AD_SCAN	Address:	1E70H
	Reset State:	0000H

The A/D scan (AD_SCAN) register allows you to select individual channels to include in the scan sequence and those to exclude. The automatic scan begins with the least-significant channel and ends with the most-significant channel.

15										8
ACH15	ACH14		ACH13		ACH12		ACH11	ACH10	ACH9	ACH8
7										0
ACH7	ACH6		ACH5		ACH4		ACH3	ACH2	ACH1	ACH0
Bit	Bit						Function
Number	Mnemonic
15:0	ACH15:0			A/D Channel x
				These bits select the channels to be included in the automatic scan.
				0 = exclude A/D channel x from scan sequence
				1 = include A/D channel x in scan sequence

Figure 12-6. A/D Scan (AD_SCAN) Register

12.4.6 Enabling the A/D Interrupt

The A/D converter can set the A/D interrupt pending bit when it completes a conversion or when the input voltage crosses the threshold value in the selected direction. To enable the interrupt, set the corresponding mask bit in the interrupt mask register (see INT_MASK on page C-33) and execute the EI instruction to globally enable servicing of interrupts. See Chapter 6, “Standard and PTS Interrupts,” for details about interrupts.

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