Digilent 410-044-10P-KIT Bedienungsanleitung PDF herunterladen (Seite 28)

28 www.xilinx.com Spartan-3 Starter Kit Board User Guide

1-800-255-7778 UG130 (v1.1) May 13, 2005

Chapter 6:

PS/2 Mouse/Keyboard Port

bidirectional keyboard communications. As shown in Figure 6-2, the attached keyboard or

mouse writes a bit on the data line when the clock signal is High, and the host reads the

data line when the clock signal is Low.

The following site contains additional information on the PS/2 bus protocol:

• PS/2 Mouse/Keyboard Protocol

http://panda.cs.ndsu.nodak.edu/~achapwes/PICmicro/PS2/ps2.htm

Keyboard

The keyboard uses open-collector drivers so that either the keyboard or the host can drive

the two-wire bus. If the host never sends data to the keyboard, then the host can use simple

input pins.

A PS/2-style keyboard uses scan codes to communicate key press data. Nearly all

keyboards in use today are PS/2 style. Each key has a single, unique scan code that is sent

whenever the corresponding key is pressed. The scan codes for most keys appear in

Figure 6-3.

If the key is pressed and held, the keyboard repeatedly sends the scan code every 100 ms or

so. When a key is released, the keyboard sends a “F0” key-up code, followed by the scan

code of the released key. The keyboard sends the same scan code, regardless if a key has

different “shift” and “non-shift” characters and regardless whether the Shift key is pressed

or not. The host determines which character is intended.

Some keys, called extended keys, send an “E0” ahead of the scan code and furthermore,

they may send more than one scan code. When an extended key is released, a “E0 F0” key-

up code is sent, followed by the scan code.

Table 6-2:

PS/2 Bus Timing

Symbol Parameter Min Max

Clock High or Low time 30 µs 50 µs

Data-to-clock setup time 5 µs 25 µs

HLD

Clock-to-data hold time 5 µs 25 µs

Figure 6-2:

PS/2 Bus Timing Waveforms

HLD

Edge 0 Edge 10

CLK (PS2C)

DATA (PS2D)

'0' start bit

'1' stop bit

UG130_c6_02_042404

1 2 ... 23 24 25 26 27 28 29 30 31 32 33 ... 63 64

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Digilent 410-044-10P-KIT Bedienungsanleitung Seite 28