HT82K628A

Rev. 1.60

5

April 16, 2004

FEH

- Resend

The host sends this command when it detects an error in

any transmission from the HT82K628A. It is sent only af-

ter a data transmission and before the host allows the

next data output. When a Resend is received, the

HT82K628A sends the previous output again (unless

the previous output was Resend, in which case the

HT82K628A sends the last byte before the Resend

command).

Commands to the Host

The following table shows the commands that the

HT82K628A may send to the host, and their hexadeci-

mal values.

Command

Hex Value

Key Detection Error/Overrun 00 (Code Set 2 and 3)

Keyboard ID

83AB

Bat Completion Code

AA

Bat Failure Core

FC

Echo

EE

Acknowledge

FA

Resend

FE

Key Detection Error/Overrun

FF (Code Set 1)

00H or FFH

- Key Detection Error

The HT82K628A sends a key detection error character if

conditions in the keyboard make it impossible to identify

a switch closure. If the HT82K628A is using scan code

set 1, the code is FFH. For sets 2 and 3, the code is 00H.

00H or FFH

- Overrun

An overrun character is placed in the HT82K628A buffer

and replaces the last code when the buffer capacity has

been exceeded. The code is sent to the host when it

reaches the top of the buffer queue. If the HT82K628A is

using scan code set 1, the code is FFH. For sets 2 and 3,

the code is 00H.

83AbH

- Keyboard ID

The keyboard ID consists of 2 bytes, Hex 83AbH. The

HT82K628A responds to the Read ID with ACK, discon-

tinues scanning and sends 2 ID bytes. The low byte is

sent first followed by the high byte. Following the output

of Keyboard ID, the HT82K628A begins scanning.

EEH

- Echo

The HT82K628A sends this code in response to an

Echo command.

AAH

- BAT Completion Code

Following satisfactory completion of the BAT, the

HT82K628A sends AAH. Any other code indicates key-

board failure.

FCH

- BAT Failure Code

If a BAT failure occurs, the HT82K628A sends this code,

discontinues scanning and waits for a host response or

reset.

FEH

- Resend

The HT82K628A issues a Resend command following

receipt of an invalid input or any input with incorrect par-

ity. If the host sends nothing to the HT82K628A, no re-

sponse is required.

Data Communications

quest to send).

yond the leading edge of the clock.

least every 60ms.

low before the tenth clock), set clock=data=high.

60ms.

vals of 10ms

board counts 11 data bits.

the falling edge

level on the

²data² line. If the line is active it is forced

to be inactive, and counts one more bit.

Note: This action signals the system that the

keyboard has received its data. Upon

reception of this signal, the system returns

to the ready state, in which it can accept

keyboard outputs or goes to the inhibit

state until it is ready.

If the keyboard

²data² line is found to be at an inactive

level following the 10th bit, a frame error has occurred,

and the keyboard continues to count until the

²data²

line becomes active. The keyboard then makes the

²data² line inactive and sends a Resend.