參數(shù)資料
型號(hào)： MM74C917
廠商： Fairchild Semiconductor Corporation
英文描述： Simplified Multi-Digit LED Display Controller(多數(shù)字式LED顯示控制器)
中文描述： 簡(jiǎn)化的多位LED顯示控制器（多數(shù)字式的LED顯示控制器）
文件頁(yè)數(shù)： 23/26頁(yè)
文件大小： 639K
代理商： MM74C917
F. Multiple Display Controllers
In systems where multiple display controllers are to be used,
the simple addressing schemes of the previous examples
may prove to be too costly in I/O capabilities, so some extra
decoding is necessary to derive the CE signals. A typical
method uses a 2–4 line decoder or a 3–8 line decoder.
Where the total time from a stable address to the write pulse
goes inactive is
≥
1 μs, a CMOS decoder such as the
MM74C42 or MM74C154 can be used, but if faster access-
ing is required, their LS equivalents should be employed.
Figure 32 shows a typical implementation of a 16-digit dis-
play using half of a DM74LS139 decoder to provide the CE
signals for each controller.
G. Making the MM74C911/MM74C912/MM74C917 Look
Like RAM
So far, the discussion of addressing the controllers has been
to separate the devices from memory, but there are certain
advantages to not doing this. In many instances, micropro-
cessor software requirements are such that data outputted
to the controller also must be remembered by the micropro-
cessor for later use. Since data cannot be read from the dis-
play controllers, the processor must also write the data in a
spare register or a memory location. This extra writing and
“bookkeeping” software can be eliminated by addressing the
MM74C911/MM74C912/MM74C917
When data is written to the controller, it could also be stored
in RAM simultaneously and can be read later by the CPU.
Figure 31 shows a simple example of this using an
MM74C912 controller and two MM2114 1k x 4 memory
chips. A DM74LS30 is used to detect when the last eight
bytes of this memory is being accessed and enables the
controller display. Thus, the last eight bytes of the RAM con-
tains a duplicate copy of what the display controller is dis-
playing.
over
existing
RAM.
IX. CONCLUSION
All three controllers provide simple and inexpensive inter-
faces to multiplexed multidigit displays. These devices are
particularly well suited to microprocessor environments, but
any type of CMOS compatible control hardware can be
used. The MM74C911/MM74C912/MM74C917 can most
easily drive common anode displays. By providing most of
the multiplex circuitry into one low-cost integrated circuit, the
burden
of
designing
discrete
eliminated.
multiplexing
has
been
AN006030-33
Port Address = 1110 11XX XABC (Binary)
(Where X = Don’t Care and AB&C are Digit Select (000–101)
FIGURE 31. MM74C912/MM74C917 to INS8060 (SC/MP) Interface
23
www.fairchildsemi.com
相關(guān)PDF資料
PDF描述
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MM74C914M Hex Schmitt Trigger with Extended Input Voltage
MM74C914N Hex Schmitt Trigger with Extended Input Voltage
MM74C922 16-Key Encoder 20-Key Encoder
相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
MM74C918 制造商:NSC 制造商全稱(chēng):National Semiconductor 功能描述:Dual CMOS 30V Relay Driver
MM74C918J 制造商:NSC 制造商全稱(chēng):National Semiconductor 功能描述:Dual CMOS 30V Relay Driver
MM74C918N 制造商:NATIONAL SEMICONDUCTOR 功能描述:SEMICONDUCTOR INTEGRATED CIRCUIT 制造商:National Semiconductor Corporation 功能描述:SEMICONDUCTOR INTEGRATED CIRCUIT
MM74C922 制造商:NSC 制造商全稱(chēng):National Semiconductor 功能描述:16, 20-Key Encoder
MM74C922N 功能描述:編碼器、解碼器、復(fù)用器和解復(fù)用器 16-Key Encoder RoHS:否 制造商:Micrel 產(chǎn)品:Multiplexers 邏輯系列:CMOS 位數(shù): 線路數(shù)量（輸入/輸出）:2 / 12 傳播延遲時(shí)間:350 ps, 400 ps 電源電壓-最大:2.625 V, 3.6 V 電源電壓-最小:2.375 V, 3 V 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:QFN-44 封裝:Tray
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