M16C User Manual.pdf

A-D ConverterMitsubishi microcomputersM16C / 62 GroupSINGLE-CHIP 16-BIT CMOS MICROCOMPUTERTable 2.7.13. Variation of the successive comparison register and Vref while A-D conversion is inprogress (8-bit mode)Successive approximation registerVref changeA-D converter stoppedb91b00 0 0 0 0 0 0 0 0VREF [V]21st comparison2nd comparison3rd comparison1n90100000000000000001st comparison resultn9 n8 1 0 0 0 0 0 0 02nd comparison resultVREF2VREF2VREF2–±±VREF2048[V]VREF VREF – [V]4 2048VREF4±n9 = 1 +n9 = 0 –VREF4VREF4n8VREF VREF= 1 +– [V]8 2048 n8 = 0 –VREF8VREF88th comparisonn9 n8 n7 n6 n5 n4 n3 1 0 0VREF2±VREF4±VREF8VREF± ...... ±256 – VREF2048[V]Conversioncompleten9 n8 n7 n6 n5 n4 n3 n2 0 0This data transfers to bit 0 tobit 7 of A-D register.Result of A-D conversionTheoretical A-D conversioncharacteristic of general 8-bitA-D converterFF16FE160316Theoretical A-D conversioncharacteristic in the 8-bit mode021601160016VREF VREF VREFx 2256 256 x 3 VREFx 4VREF256 256 x 254 VREF0 x 255 VREF256 x 1 256VREFAnalog input voltage2048 x 3Figure 2.7.25. Theoretical A-D conversion characteristics (8-bit mode)408