PIC16C76-04E/SP View Datasheet(PDF) - Microchip Technology
Part Name
Description
Manufacturer
PIC16C76-04E/SP Datasheet PDF : 288 Pages
| |||
PIC16C7X
13.2
Selecting the A/D Conversion Clock
Applicable Devices
72 73 73A 74 74A 76 77
The A/D conversion time per bit is defined as TAD. The
A/D conversion requires 9.5TAD per 8-bit conversion.
The source of the A/D conversion clock is software
selectable. The four possible options for TAD are:
• 2TOSC
• 8TOSC
• 32TOSC
• Internal RC oscillator
For correct A/D conversions, the A/D conversion clock
(TAD) must be selected to ensure a minimum TAD time
of 1.6 µs.
Table 13-1 shows the resultant TAD times derived from
the device operating frequencies and the A/D clock
source selected.
13.3
Configuring Analog Port Pins
Applicable Devices
72 73 73A 74 74A 76 77
The ADCON1, TRISA, and TRISE registers control the
operation of the A/D port pins. The port pins that are
desired as analog inputs must have their correspond-
ing TRIS bits set (input). If the TRIS bit is cleared (out-
put), the digital output level (VOH or VOL) will be
converted.
The A/D operation is independent of the state of the
CHS2:CHS0 bits and the TRIS bits.
Note 1: When reading the port register, all pins
configured as analog input channels will
read as cleared (a low level). Pins config-
ured as digital inputs, will convert an ana-
log input. Analog levels on a digitally
configured input will not affect the conver-
sion accuracy.
Note 2: Analog levels on any pin that is defined as
a digital input (including the AN7:AN0
pins), may cause the input buffer to con-
sume current that is out of the devices
specification.
TABLE 13-1: TAD vs. DEVICE OPERATING FREQUENCIES
AD Clock Source (TAD)
Device Frequency
Operation
ADCS1:ADCS0
20 MHz
5 MHz
1.25 MHz
333.33 kHz
2TOSC
00
100 ns(2)
400 ns(2)
1.6 µs
6 µs
8TOSC
01
400 ns(2)
1.6 µs
6.4 µs
24 µs(3)
32TOSC
10
1.6 µs
6.4 µs
25.6 µs(3)
96 µs(3)
RC(5)
11
2 - 6 µs(1,4)
2 - 6 µs(1,4)
2 - 6 µs(1,4)
2 - 6 µs(1)
Legend: Shaded cells are outside of recommended range.
Note 1: The RC source has a typical TAD time of 4 µs.
2: These values violate the minimum required TAD time.
3: For faster conversion times, the selection of another clock source is recommended.
4: When device frequency is greater than 1 MHz, the RC A/D conversion clock source is recommended for
sleep operation only.
5: For extended voltage devices (LC), please refer to Electrical Specifications section.
© 1997 Microchip Technology Inc.
DS30390E-page 121
Share Link: 