參數(shù)資料
型號(hào): AD7938BCPZ
廠商: Analog Devices Inc
文件頁數(shù): 19/36頁
文件大?。?/td> 0K
描述: IC ADC 12BIT 8CH 1.5MSPS 32LFCSP
標(biāo)準(zhǔn)包裝: 1
位數(shù): 12
采樣率(每秒): 1.5M
數(shù)據(jù)接口: 并聯(lián)
轉(zhuǎn)換器數(shù)目: 1
功率耗散(最大): 13.5mW
電壓電源: 單電源
工作溫度: -40°C ~ 85°C
安裝類型: 表面貼裝
封裝/外殼: 32-VFQFN 裸露焊盤,CSP
供應(yīng)商設(shè)備封裝: 32-LFCSP-VQ
包裝: 托盤
輸入數(shù)目和類型: 8 個(gè)單端,單極;4 個(gè)差分,單極;4 個(gè)偽差分,單極;7 偽差分,單極
配用: EVAL-AD7938CBZ-ND - EVAL BOARD FOR AD7938
AD7938/AD7939
Data Sheet
Rev. C | Page 26 of 36
Reading Data from the AD7938/AD7939
With the W/B pin tied logic high, the AD7938/AD7939
interface operates in word mode. In this case, a single read
operation from the device accesses the conversion data-word
on Pins DB0/DB2 to Pin DB11. The DB8/HBEN pin assumes
its DB8 function. With the W/B pin tied to logic low, the
AD7938/AD7939 interface operates in byte mode. In this case,
the DB8/HBEN pin assumes its HBEN function. Conversion
data from the AD7938/AD7939 must be accessed in two read
operations with eight bits of data provided on DB0 to DB7 for
each of the read operations. The HBEN pin determines whether
the read operation accesses the high byte or the low byte of the
12-bit or 10-bit word. For a low byte read, DB0 to DB7 provide
the eight LSBs of the 12-bit word. For 10-bit operation, the two
LSBs of the low byte are 0s, followed by six bits of conversion
data. For a high byte read, DB0 to DB3 provide the four MSBs
of the 12-bit or10-bit word. DB5 to DB7 of the high byte
provide the channel ID. Figure 36 shows the read cycle timing
diagram for a 12-bit or 10-bit transfer. When operating in word
mode, the HBEN input does not exist, and only the first read
operation is required to access data from the device. When
operating in byte mode, the two read cycles shown in Figure 37
are required to access the full data-word from the device.
The CS and RD signals are gated internally and the level is
triggered active low. In either word mode or byte mode, CS and
RD can be tied together because the timing specifications for t10
and t11 are 0 ns minimum. This means the bus is constantly
driven by the AD7938/AD7939.
The data is placed onto the data bus a time t13 after both CS and
RD go low. The RD rising edge can be used to latch data out of
the device. After a time, t14, the data lines become three-stated.
Alternatively, CS and RD can be tied permanently low and the
conversion data is valid and placed onto the data bus a time, t9,
before the falling edge of BUSY.
Note that if RD is pulsed during the conversion time, this
causes a degradation in linearity performance of approximately
0.25 LSB. Reading during conversion by way of tying CS and
RD low does not cause any degradation.
t11
t10
t13
t15
t16
t14
t12
t17
LOW BYTE
HIGH BYTE
DB0 TO DB7
HBEN/DB8
RD
CS
03715-
005
Figure 37. AD7938/AD7939 Parallel Interface—Read Cycle Timing for Byte Mode Operation (W/B = 0)
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