Datasheet

Chapter 10 Analog-to-Digital Converter (S08ADC12V1)
MC9S08DZ60 Series Data Sheet, Rev. 4
174 Freescale Semiconductor
10.1.3 Alternate Clock
The ADC module is capable of performing conversions using the MCU bus clock, the bus clock divided
by two, the local asynchronous clock (ADACK) within the module, or the alternate clock, ALTCLK. The
alternate clock for the MC9S08DZ60 Series MCU devices is the external reference clock (MCGERCLK).
The selected clock source must run at a frequency such that the ADC conversion clock (ADCK) runs at a
frequency within its specified range (f
ADCK
) after being divided down from the ALTCLK input as
determined by the ADIV bits.
ALTCLK is active while the MCU is in wait mode provided the conditions described above are met. This
allows ALTCLK to be used as the conversion clock source for the ADC while the MCU is in wait mode.
ALTCLK cannot be used as the ADC conversion clock source while the MCU is in either stop2 or stop3.
10.1.4 Hardware Trigger
The ADC hardware trigger, ADHWT, is the output from the real time counter (RTC). The RTC counter
can be clocked by either MCGERCLK or a nominal 1 kHz clock source.
The period of the RTC is determined by the input clock frequency, the RTCPS bits, and the RTCMOD
register. When the ADC hardware trigger is enabled, a conversion is initiated upon an RTC counter
overflow.
The RTC can be configured to cause a hardware trigger in MCU run, wait, and stop3.
Table 10-1. ADC Channel Assignment
ADCH Channel Input
00000 AD0 PTA0/ADP0/MCLK
00001 AD1 PTA1/ADP1/ACMP1+
00010 AD2 PTA2/ADP2/ACMP1P-
00011 AD3 PTA3/ADP3/ACMP1O
00100 AD4 PTA4/ADP4
00101 AD5 PTA5/ADP5
00110 AD6 PTA6/ADP6
00111 AD7 PTA7/ADP7
01000 AD8 PTB0/ADP8
01001 AD9 PTB1/ADP9
01010 AD10 PTB2/ADP10
01011 AD11 PTB3/ADP11
01100 AD12 PTB4/ADP12
01101 AD13 PTB5/ADP13
01110 AD14 PTB6/ADP14
01111 AD15 PTB7/ADP15
10000 AD16 PTC0/ADP16
10001 AD17 PTC1/ADP17
10010 AD18 PTC2/ADP18
10011 AD19 PTC3/ADP19
10100 AD20 PTC4/ADP20
10101 AD21 PTC5/ADP21
10110 AD22 PTC6/ADP22
10111 AD23 PTC7/ADP23
11000– AD24 through AD25 Reserved
11001
11010 AD26 Temperature Sensor
1
11011 AD27 Internal Bandgap
2
11100 Reserved Reserved
11101
V
REFH
V
REFH
11110 V V
ADCH Channel Input