The A/D conversion time per bit i" />
參數(shù)資料
型號: PIC18F252T-E/SO
廠商: Microchip Technology
文件頁數(shù): 117/134頁
文件大小: 0K
描述: IC MCU CMOS 40MHZ 16K FLSH28SOIC
標(biāo)準(zhǔn)包裝: 1,600
系列: PIC® 18F
核心處理器: PIC
芯體尺寸: 8-位
速度: 40MHz
連通性: I²C,SPI,UART/USART
外圍設(shè)備: 欠壓檢測/復(fù)位,LVD,POR,PWM,WDT
輸入/輸出數(shù): 23
程序存儲器容量: 32KB(16K x 16)
程序存儲器類型: 閃存
EEPROM 大小: 256 x 8
RAM 容量: 1.5K x 8
電壓 - 電源 (Vcc/Vdd): 4.2 V ~ 5.5 V
數(shù)據(jù)轉(zhuǎn)換器: A/D 5x10b
振蕩器型: 外部
工作溫度: -40°C ~ 125°C
封裝/外殼: 28-SOIC(0.295",7.50mm 寬)
包裝: 帶卷 (TR)
1997 Microchip Technology Inc.
DS30444E - page 83
PIC16C9XX
12.2
Selecting the A/D Conversion Clock
The A/D conversion time per bit is dened as TAD. The
A/D conversion requires 9.5 TAD per 8-bit conversion.
The source of the A/D conversion clock is software
selected. 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
s.
Table 12-1 shows the resultant TAD times derived from
the device operating frequencies and the A/D clock
source selected.
12.3
Conguring Analog Port Pins
The ADCON1 and TRISA registers control the opera-
tion of the A/D port pins. The port pins that are desired
as analog inputs must have their corresponding TRIS
bits set (input). If the TRIS bit is cleared (output), 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
congured as analog inputs will read as
cleared (a low level). Pins congured as
digital inputs, will convert an analog input.
Analog levels on a digitally congured
input will not affect the conversion accu-
racy.
Note 2: Analog levels on any pin that is dened as
a digital input (including the AN4:AN0
pins), may cause the input buffer to con-
sume current that is out of the devices
specication.
TABLE 12-1: TAD vs. DEVICE OPERATING FREQUENCIES
A/D Clock Source (TAD)
Device Frequency
Operation
ADCS1:ADCS0
8 MHz
5 MHz
1.25 MHz
333.33 kHz
2TOSC
00
250 ns(2)
400 ns(2)
1.6
s
6
s
8TOSC
01
1
s
1.6
s
6.4
s
24
s(3)
32TOSC
10
4
s
6.4
s
25.6
s(3)
96
s(3)
RC
11
2 - 6
s(1,4)
2 - 6
s(1,4)
2 - 6
s(1,4)
2 - 6
s(1)
Legend: Shaded cells are outside of recommended range.
Note 1: The RC source has a typical TAD time of 4
s.
2: These values violate the minimum required TAD time.
3: For faster conversion times, the selection of another clock source is recommended.
4: When derived frequency is greater than 1 MHz, the RC A/D conversion clock source is recommended for
sleep mode only
5: For extended voltage devices (LC), please refer to the electrical specications section.
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