vt82c42 ETC-unknow, vt82c42 Datasheet - Page 3

• Manufacturer Part Number: vt82c42
• Description: Vt82c42 Keyboard Controller
• Manufacturer: ETC-unknow

1. General Overview:
The VT82C42 is a compatible direct replacement for the Intel 80C42 BIOS version of the Keyboard
Controller. The VT82C42 is fully implemented by hardware logic so that it has a very fast response capability
for any command issued by the host. In addition to keyboard support, the VT82C42 also offers PS/2 mouse
support. The VT82C42 also offers the Mouse Lock
designed by VIA technologies, which locks the mouse when the keylock function is initiated.
2. Features:
3. Function Description:
The internal timer counting is based on an 8Mhz clock input from X1, X2 ( or X2, with X1 connected to
ground). After the deassertion of RESET#, the VT82C42 will drive high at pin P23 and pin P27. After 6 s (6
x 8 clocks) of driving, the VT82C42 will check on pins T1 & P10; if both pins are low, then the VT82C42
will switch to PS/2 mode. Otherwise, the VT82C42 will remain in AT mode.
If the VT82C42 is in AT mode after the self test, then it will drive P24 and P25 low with all other ports high.
If the VT82C42 is in PS/2 mode, then it will drive P24, P25, P22, and P27 low with all other ports high. The
VT82C42 will not change its driving value until it receives the command "AA" from the host. When receiving
the command "AA" from the host, the VT82C42 will prepare a "55" in its output buffer and drive P24
(reflecting the internal OBF flag) high within 6 clocks. This response time is the typical active time for
internal IBF flag. After this initialization procedure, the VT82C42 will drive P26 low (AT mode) or drive P26
and P23 low (PS/2 mode) in order for the keyboard and mouse interface to receive data from keyboard or
mouse.
When the keyboard or mouse toggles the interface (KBCLK, KBDATA, MSCLK,MSDATA), the controller
receives data from the serial interface and stores the received data into its internal output buffer. If the
received data is from the keyboard, a scan code translation is executed before the data is sent to the output
buffer. The VT82C42 also raises P24 or P25 to indicate a output buffer full. The host is signaled to issue a
read command to the data port to read the received data out. When the VT82C42 receives data in the normal
mode (pin 25 on DIP40 or pin 28 on PLCC44 parts connected to VCC) and the status of P17 is low, then the
controller will not raise the P24, nor activate its internal OBF flag. It looks like the controller will consume the
income data itself. And if the data is from the mouse, the controller will still raise P25 to indicate that data is
coming from mouse. However, if the VT82C42 is in Mouse Lock
PLCC44 parts connected to GND), the data from either keyboard or mouse will be prohibited from sending to
the host.
VIA Technologies, Inc.
Fully hardware implemented, 0.8 m CMOS Technology.
Very high speed response of A20 GATE & reset.
Support PS2 style mouse.
Compatible with all major BIOS, including AWARD, PHOENIX and AMI.
40 pin PDIP and 44 pin PLCC packages.
VT82C42 Keyboard Controller
-1-
TM
function (patent pending), a feature exclusively
TM
mode (pin 25 on DIP40 or pin 28 on
Date : November 22, 1995
VT82C42