參數(shù)資料
型號: SN74HC161DRG4
廠商: TEXAS INSTRUMENTS INC
元件分類: 計數(shù)器
英文描述: HC/UH SERIES, SYN POSITIVE EDGE TRIGGERED 4-BIT UP BINARY COUNTER, PDSO16
封裝: GREEN, PLASTIC, MS-012AC, SOIC-16
文件頁數(shù): 4/27頁
文件大?。?/td> 886K
代理商: SN74HC161DRG4
SN54HC161, SN74HC161
4BIT SYNCHRONOUS BINARY COUNTERS
SCLS297D JANUARY 1996 REVISED SEPTEMBER 2003
12
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
APPLICATION INFORMATION
The glitch on RCO is caused because the propagation delay of the rising edge of QA of the second stage is
shorter than the propagation delay of the falling edge of ENT. RCO is the product of ENT, QA, QB, QC, and QD
(ENT
× QA × QB × QC × QD). The resulting glitch is about 712 ns in duration. Figure 3 shows the condition in
which the glitch occurs. For simplicity, only two stages are being considered, but the results can be applied to
other stages. QB, QC, and QD of the first and second stage are at logic one, and QA of both stages are at logic
zero (1110 1110) after the first clock pulse. On the rising edge of the second clock pulse, QA and RCO of the
first stage go high. On the rising edge of the third clock pulse, QA and RCO of the first stage return to a low level,
and QA of the second stage goes to a high level. At this time, the glitch on RCO of the second stage appears
because of the race condition inside the chip.
12
3
4
5
CLK
ENT1
QB1, QC1, QD1
QA1
RCO1, ENT2
QB2, QC2, QD2
QA2
RCO2
Glitch (712 ns)
Figure 3
The glitch causes a problem in the next stage (stage three) if the glitch is still present when the next rising clock
edge appears (clock pulse 4). To ensure that this does not happen, the clock frequency must be less than the
inverse of the sum of the clock-to-RCO propagation delay and the glitch duration (tg). In other words,
fmax = 1/(tpd CLK-to-RCO + tg). For example, at 25°C at 4.5-V VCC, the clock-to-RCO propagation delay is
43 ns and the maximum duration of the glitch is 12 ns. Therefore, the maximum clock frequency that the
cascaded counters can use is 18 MHz. The following tables contain the fclock, tw, and fmax specifications for
applications that use more than two ’HC161 devices cascaded together.
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