參數(shù)資料
型號(hào)： PCPIC
英文描述： PC(ISA)BUS I/O CARD
中文描述： 電腦（ISA）總線(xiàn)的I / O卡
文件頁(yè)數(shù)： 22/40頁(yè)
文件大?。?/td> 468K
代理商： PCPIC
2192-09155-000-000
that some languages cannot use 16-bit integers because one bit is
used for the sign. You may have to do your arithmetic in floating-
point if this is the case.
The frequency in kHz is the number of counts in 10 ms divided by
10. This timebase value will overflow at input frequencies above
6.5MHz.
Counting
Counting is much simpler than measuring frequency. There is no
timebase to set up and several count modes are possible. The PCPIC
has three ways of gating counters - not at all (PCPIC counter control
bits 000), with one gate input per counter on group 2 (PCPIC counter
control bits 100), and with a start count input per counter on group
2 and a stop count input per counter on group 3 (PCPIC counter
control bits 110). The start and stop inputs are active-low, and are
pulled high with resistors when unconnected. If you are using the
start-stop method note that the start and stop inputs are setting and
resetting flip-flops. In other words pulling a group 2 input (for
example wire 23 of the ribbon-cable) low momentarily opens the
counter gate and leaves it open until the flip-flop is reset. There are
three ways to reset the flip-flop. One is to pull the corresponding
group 3 input low with an external signal (in this case on wire 33 on
the ribbon-cable), and another is to pull it low by writing a 1 bit to
the corresponding group 3 output. These outputs are connected to
the latch at pointer 0CH by inverting buffers. By the same token you
must ensure that the group 3 outputs are high (that is, you have
written 0 to them) if you wish to use inputs on group 3 to reset the
flip-flops. The third way is to write 001(binary) to the counter
control bits, then rewrite the counter control bits to put the counters
back into the active mode.Because the flip-flops and the group 3
outputs power-up in a random state it is good practice to reset them
before use.
The following example shows how to count pulses on wire 3 of the
ribbon- cable for a time defined as the time between wire 23 going
low briefly and wire 33 going low.
Write D8H to pointer 12H to set the board control register
Write 70H to pointer 3 to put counter 0 into mode 0
Write FFH to pointer 1 to define the less-significant count byte an
stop the counter
Write 01 to pointer 0CH to reset the input flip-flop
Write 00 to pointer 0CH to enable the input flip-flop
Write FFHto pointer 1 to define the more-significant count byte
and enable the counter
Wire 23 goes low then high, then wire 33 goes low then high
Check for a null count, as described on the previous page, then read
counter 0 to see how many counts have accumulated
J230 PCPIC
Page 22
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PCPKITIW 功能描述:電線(xiàn)導(dǎo)管 Pan Pole Replacement Parts Kit (includes RoHS:否 制造商:Panduit 類(lèi)型:Slotted SideWall Open finger design wiring cut 材料:Polypropylene 顏色:Light Gray 大小: 最大光束直徑: 抗拉強(qiáng)度: 外部導(dǎo)管寬度:25 mm 外部導(dǎo)管高度:25 mm
PCPL-17B 制造商:PMA 功能描述:20MM POLY. BLK CONT. PACK
PCPLHK 功能描述:ANT SUB YAGI 10-13 ELEMENT KIT RoHS:是 類(lèi)別:RF/IF 和 RFID >> RF 天線(xiàn) 系列:* 標(biāo)準(zhǔn)包裝:1 系列:*
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