Thursday, December 23, 2010

Weak current College】 【LED dot matrix display principle】.

Dot-matrix display principle
1. a lattice theory
The internal structure and appearance of dot matrix as follows, 8X8 dot matrix consists of 64 LEDs, and each led is placed in row and column intersection of the line, when the corresponding row 1 level, a column resets the level 0, the corresponding led will light up; if you want to be a shining, 9 feet meet high level 13 feet after low level, the first point is bright; if you want the first line of light, 9 feet to meet high level, but (13, 3, 4, 6, 10, 11, 15, 16) these pins received low level, then the first row will light up; if you want the first column, then the 13 foot, received low level (9, 14, 8, 12, 1, 7, 2, 5) by the high level, then first columns will be lit.

In general we use dot-matrix display Chinese characters are used in 16 * 16 dot matrix songtizi library, so-called 16 * 16, every character in the longitudinal and transverse the 16 points displayed in the region. In other words, it is imperative to use four 8 * 8 array into a matrix of 16 * 16. As shown in the following illustration, to display the "you" and the corresponding point on the points of light, because our dot matrix columns line is a low level in force, and in line line is high level work, so to display the word "you", it's bit code information to negated that all columns (13 ~ 16 feet) (1111011101111111, 0xF7, 0x7F), and the first row (9 feet) get 1 signal, then the first row returned 0. Then sent a second row to display data (13 ~ 16 feet) (1111011101111111, 0xF7, 0x7F), while the second row (14 feet) get 1 signal. And so on, as long as each row data display interval is short, make use of the human eye Visual effects, so send paused 16 16 rows scanned data will see a "you"; the second send data is sent to the line matrix signal line then scan column line is the same reason. Similarly to the word "you", 16 rows (9, 14, 8, 12, 1, 7, 2, 5) sent (0x00, 0x00, 0000000000000000) and the first column (13 feet) and "0". In the same vein scanning the second column. When the line wire sent 16 data column line scan 16 after a word "you" is displayed.

2. transposition latch 74ls595 principle
74ls595 as 8-bit output latch shift register
RESET: reset signal
Shitfclock: shift clock
Serialdatainput: serial data input
Outputenable: output enable
Latchclock: latch clock
3-layer structure 595:
The first layer to shift D triggers;
The second layer is the latch trigger; D
The third layer is a 3-state output;
When the reset signal is 0, the shift 0 D flip-flop Ching;
When shift pulse > from L-H, the first shift D triggers Q = D;
Other Qn = Qn-1;
When the latch pulse from 0-> 1, the second layer is latched D trigger output =/input;
When OE = 1, 595 output for high-impedance state;
When OE = 0, 595 output is the second-tier to latch trigger output D reversed phase;

The data side: 74595
QA--QH: eight-bit parallel output, you can add dot-matrix 8 columns.
QH ': cascade output. It took a Si-595.
SI: serial data input.

74595 control-description:
/SCLR (10 feet): low level will shift register data is cleared to zero. Typically, it received the Vcc.
SCK (11 feet): rising edge data registers data when displaced. QA--> QB--> > QC--...--> QH; falling edge shift register data unchanged. (Pulse width: 5V, greater than tens of nanoseconds. Typically selected microsecond)
RCK (12 feet): rising edge at the time of the shift register data into the data storage registers, falling edge, storage registers data unchanged. Usually the RCK reset to low level, when the transfer is finished, in the end-result in a positive RCK pulse (5V, greater than tens of nanoseconds. Typically selected microsecond), update the display of data.
/G (13 feet): high level prevents output (high resistance State). If the SCM pin not nervous, use a PIN to control it, you can easily create blinking and turns off the effect. Than through data-transfer control to save time and effort.
Note: 74164 and 74595 function is similar, is 8-bit serial input go parallel output shift register. 74164 drive current (25mA) than 74595 (35mA) to small, 14 foot package, the volume is also smaller.
The main advantage is 74595 with data storage registers, in shift, the output data can remain unchanged. This serial slow occasion useful, no HDTV digital tube.
And 164 only data cleared end more than 595 with output to/ban control side, you can make the output is high impedance state.
4953 principle
4953 is double-MOS package together, dot-matrix display in its effect is selected, the dot-matrix display we will all corresponding dot matrix row cable is connected together so that you have 16 rows, you will want to use eight 4953. It's 1 foot and leg power 3, 7, 8 next, 5, 6, add. When the row selected signal to make the 2 foot level decreases, so will and 1 foot 7-, 8-pin will appear on-so one row. When the row selected signal to make the 4 foot level decreases, so 3 feet and the 5, 6 feet on showing another row.

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