UR5HC418 Datasheet, PDF (5/14 Pages) Semtech Corporation – AT / PS/2 - Compatible Keyboard Encoder

8042 EMULATION CHANNEL
The DeskCoder^TM fully emulates a
system’s keyboard port, available to
a standard 84/85/101/102 external
keyboard or other 8042-compatible
device. Communication with a
keyboard-compatible device is
accomplished by clock and data
lines via EKC and EKD pins,
respectively. A third pin, EKC1 that
connects to the clock line, interrupts
the controller whenever the external
device initiates a communication
session. When power is first
applied, the controller proceeds
with the standard reset sequence
with the external device. Data and
commands initiated from the
external device are buffered in the
controller’s FIFO along with data
from the scanned matrix, and then
are presented to the system as if
they were coming from a single
source. Once they are
acknowledged, commands and
data from the system are then
transmitted to the external device.
PC COMMUNICATION
The DeskCoder^TM implements all
the standard functions of
communication with a BIOS-
compatible PC/XT or AT/PS/2 host
system. Two lines, KC and KD,
provide bi-directional clock and
data signals. In addition, the
DeskCoder^TM supports all
commands from and to the system,
as described in the IBM Technical
Reference Manuals.
The following table shows the
commands that the system may
send and their values in
hexadecimal.
Command
Hex Value
Set/Reset Status
ED
Indicators
Echo
EE
Invalid Command
EF
Select Alternate
F0
Scan Codes
Invalid Command
F1
Read ID
F2
Set Typematic
F3
Rate/Delay
Enable
F4
Default Disable
F5
Set Default
F6
Set All Keys
Typematic
F7
Make/Break
F8
Make
F9
Typematic/Make/Break FA
Set Key Type
Typematic
FB
Make/Break
FC
Make
FD
Resend
FE
Reset
FF
Table 2: Keyboard Commands from the
System (AT / PS/2 protocol)
The following table shows the
commands that the keyboard may
send to the system.
Command
Hex Value
Key Detection
00*
Error/Overrun
Keyboard ID
83AB
BAT Completion Code
AA
BAT Failure Code
FC
Echo
EE
Acknowledge (Ack)
FA
Resend
FE
Key Detection
Error/Overrun
FF**
*Code Sets 2 and 3
**Code Set 1
Table 3: Keyboard Commands to the
System (AT/PS/2 protocol)
When an external keyboard is
connected, commands from the
system are also directed to the
external keyboard. Presence or
absence of an external device does
not affect the normal operation of
the UR5HC418.
These commands are supported in
the AT / PS/2 protocol and can be
sent to the keyboard at any time.
Copyright ©1997-2001 Semtech Corporation
5
DOC5-418-DS-109
www.semtech.com