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80C550 Datasheet(PDF) 9 Page - NXP Semiconductors |
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80C550 Datasheet(HTML) 9 Page - NXP Semiconductors |
9 / 28 page Philips Semiconductors Product specification 80C550/83C550/87C550 80C51 8-bit microcontroller family 4K/128 OTP/ROM/ROMless, 8 channel 8 bit A/D, watchdog timer 1998 May 01 9 Sample A/D Routines The following routines demonstrate two methods of operating the A/D converter. The first method uses polling to determine when the A/D conversion is complete. The second method uses the A/D interrupt to flag the end of conversion. The routine ReadAD will start a read of the A/D channel identified by R7, and wait for the conversion to complete, polling the A/D interrupt flag. The result is returned in the accumulator. ReadAD:MOV A,#08h ;Basic A/D start command. ORL A,R7 ;Add channel # to be read. MOV ADCON,A; ;Start A/D. ADLoop: MOV A,ADCON ;Get A/D status. JNB ACC.4,ADLoop;Wait for ADCI (A/D ;finished). MOV A,ADAT ;Get conversion result MOV ADCON,#0 ;Clear ADCI. RET The routine StartAD will start a read of the A/D channel identified by R7 and exit back to the calling program. When the conversion is complete, the A/D interrupt occurs, calling the A/D interrupt service routine. The result of the conversion is returned in register R6. StartAD: MOV A,#08h ;Basic A/D start command. ORL A,R7 ;Add channel # to be read. MOV ADCON,A ;Start A/D. RET . . . ORG 2Bh ;A/D interrupt address. ADInt: MOV R6,ADAT ;Get conversion result. MOV ADCON,#0 ;Clear ADCI. RETI RS VANALOG INPUT CS CC To Comparator + IN IN+1 SmN+1 SmN RmN+1 RmN Multiplexer Rm = 0.5 - 3 k Ω CS + CC = 15pF maximum RS = Recommended < 9.6 k Ω for 1 LSB @ 12MHz NOTE: Because the analog to digital converter has a sampled-data comparator, the input looks capacitive to a source. When a conversion is initiated, switch Sm closes for 8tcy (8 µs @ 12MHz crystal frequency) during which time capacitance Cs + Cc is charged. It should be noted that the sampling causes the analog input to present a varying load to an analog source. SU00199 Figure 3. A/D Input: Equivalent Circuit |
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