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Application Description
Question 1
When using the HT82K629A for USB keyboard applications, can special function keys be defined?
Answer
Yes, this is possible. The HT82K629's multimedia keys have 5 functions, Explorer, Screen Save, Record, Rewind and Minimise, which can be used to define special functions. If this is done, it is necessary for users to write their own PC client application USB drivers. The internal Microsoft KB driver cannot be used.
Question 2
Under what circumstances will the HT82K628A transmit "AA" to the PC?
Answer
Under the following reset conditions the HT82K628A will transmit "AA" to the PC.
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A normal power on reset condition.
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If the RES line on the device is pulled low
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If a Low-voltage Reset condition is reached, that is if the Vdd voltage is less than 2.4V, then the internal LVR circuit will transmit "AA" to the PC
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If the Watch Dog Timer is activated. If the device receives noise over the accepted noise threshold, then the firmware may enter a loop or enter an undefined condition, when this happens the WDT internal circuit will reset the IC and will transmit "AA" to the PC.
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If the PC sends an "FF" instruction to the device, then the device will respond by transmitting "AA" to the PC
Others
Question 1
How can the Keyboard/Mouse devices for the PS/2 interface be connected to the USB interface? Does the circuit board need to be changed or is it possible to just change the PS/2 plug to a USB type?
Answer
The PS/2 and USB are two very different types of interfaces with totally different data protocols. Holtek Keyboard/Mouse devices basically are divided into two categories. The first category is the USB+PS/2 devices, such as the HT82M98A and HT82K629A devices, which can automatically detect if the connected interface is a USB type or PS/2 type. Upon detection the devices will then transmit the corresponding correct USB or PS/2 signals. The circuit hardware to implement both types of interface is the same, details of which are given in the Application Circuit in the corresponding datasheet. For most applications a USB plug is supplied as standard and an adapter plug supplied along with the products to enable the user to change to a PS/2 interface if required. In the other device category are the PS/2 devices, such as theHT82M39A and HT82K628A devices, which can only be used with PS/2 interfaces. It is not possible to connect these devices to a USB interface by making circuit board modifications or by using an adapter plug.
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