Datasheet

© 2010 Microchip Technology Inc. DS70135G-page 145
dsPIC30F4011/4012
20.7.1.3 1 Msps Configuration Items
The following configuration items are required to
achieve a 1 Msps conversion rate.
• Comply with conditions provided in Table 20-2
• Connect external V
REF+ and VREF- pins following
the recommended circuit shown in Figure 20-2
• Set SSRC<2:0> = 111 in the ADCON1 register to
enable the auto-convert option
• Enable automatic sampling by setting the ASAM
control bit in the ADCON1 register
• Enable sequential sampling by clearing the
SIMSAM bit in the ADCON1 register
• Enable at least two sample and hold channels by
writing the CHPS<1:0> control bits in the
ADCON2 register
• Write the SMPI<3:0> control bits in the ADCON2
register for the desired number of conversions
between interrupts. At a minimum, set SMPI<3:0>
= 0001 since at least two sample and hold chan-
nels should be enabled
• Configure the A/D clock period to be:
by writing to the ADCS<5:0> control bits in the
ADCON3 register
• Configure the sampling time to be 2 T
AD by
writing: SAMC<4:0> = 00010
• Select at least two channels per analog input pin
by writing to the ADCHS register
20.7.2 750 ksps CONFIGURATION
GUIDELINE
The following configuration items are required to
achieve a 750 ksps conversion rate. This configuration
assumes that a single analog input is to be sampled.
• Comply with conditions provided in Table 20-2
• Connect external V
REF+ and VREF- pins following
the recommended circuit shown in Figure 20-2
• Set SSRC<2:0> = 111 in the ADCON1 register to
enable the auto-convert option
• Enable automatic sampling by setting the ASAM
control bit in the ADCON1 register
• Enable one sample and hold channel by setting
CHPS<1:0> = 00 in the ADCON2 register
• Write the SMPI<3:0> control bits in the ADCON2
register for the desired number of conversions
between interrupts
• Configure the A/D clock period to be:
by writing to the ADCS<5:0> control bits in the
ADCON3 register
• Configure the sampling time to be 2 T
AD by
writing: SAMC<4:0> = 00010
20.7.3 600 ksps CONFIGURATION
GUIDELINE
The configuration for 600 ksps operation is dependent
on whether a single input pin is to be sampled or
whether multiple pins are to be sampled.
20.7.3.1 Single Analog Input
When performing conversions at 600 ksps for a single
analog input, at least two sample and hold channels
must be enabled. The analog input multiplexer must be
configured so that the same input pin is connected to
both sample and hold channels. The ADC converts the
value held on one S/H channel, while the second S/H
channel acquires a new input sample.
20.7.3.2 Multiple Analog Input
The ADC can also be used to sample multiple analog
inputs using multiple sample and hold channels. In this
case, the total 600 ksps conversion rate is divided
among the different input signals. For example, four
inputs can be sampled at a rate of 150 ksps for each
signal or two inputs can be sampled at a rate of
300 ksps for each signal. Sequential sampling must be
used in this configuration to allow adequate sampling
time on each input.
20.7.3.3 600 ksps Configuration Items
The following configuration items are required to
achieve a 600 ksps conversion rate.
• Comply with conditions provided in Table 20-2
• Connect external V
REF+ and VREF- pins following
the recommended circuit shown in Figure 20-2
• Set SSRC<2:0> = 111 in the ADCON1 register to
enable the auto-convert option
• Enable automatic sampling by setting the ASAM
control bit in the ADCON1 register
• Enable sequential sampling by clearing the
SIMSAM bit in the ADCON1 register
• Enable at least two sample and hold channels by
writing the CHPS<1:0> control bits in the
ADCON2 register
• Write the SMPI<3:0> control bits in the ADCON2
register for the desired number of conversions
between interrupts. At a minimum, set
SMPI<3:0> = 0001 since at least two sample and
hold channels should be enabled
• Configure the A/D clock period to be:
by writing to the ADCS<5:0> control bits in the
ADCON3 register
• Configure the sampling time to be 2 T
AD by
writing: SAMC<4:0> = 00010
Select at least two channels per analog input pin by
writing to the ADCHS register.
1
12 x 1,000,000
= 83.33 ns
1
(12 + 2) x 750,000
= 95.24 ns
1
12 x 600,000
= 138.89 ns