FEATURES
: ∗ Fully hardware implemented, 0.8µm 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. 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 µs (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.
VIA
