ht82m99e Holtek Semiconductor Inc., ht82m99e Datasheet - Page 10

• Manufacturer Part Number: ht82m99e
• Description: Ht82m99e/ht82m99a -- Usb Mouse Encoder 8-bit Mcu
• Manufacturer: Holtek Semiconductor Inc.

The USB interrupts are triggered by the following USB
events and the related interrupt request flag (USBF; bit
4 of the INTC) will be set.
When the interrupt is enabled, the stack is not full and
the external interrupt is active, a subroutine call to loca-
tion 04H will occur. The interrupt request flag (USBF)
and EMI bits will be cleared to disable other interrupts.
When the PC Host access the FIFO of the HT82M99E/
HT82M99A, the corresponding request bit of the USR is
set, and a USB interrupt is triggered. So user can easily
decide which FIFO is accessed. When the interrupt has
been served, the corresponding bit should be cleared by
firmware. When the HT82M99E receives a USB Sus-
pend signal from the Host PC, the suspend line (bit0 of
the USC) of the HT82M99E is set and a USB interrupt is
also triggered.
When the HT82M99E/HT82M99A receives a Resume
signal from the Host PC, the resume line (bit3 of the
USC) of the HT82M99E/HT82M99A are set and a USB
interrupt is triggered.
Whenever a USB reset signal is detected, the USB in-
terrupt is triggered and URST_Flag bit of the USC regis-
ter is set. When the interrupt has been served, the bit
should be cleared by firmware.
The internal timer/even counter interrupt is initialized by
setting the timer/event counter interrupt request flag (;bit
6 of the INTC), caused by a timer overflow. When the in-
terrupt is enabled, the stack is not full and the TF is set, a
subroutine call to location 0CH will occur. The related in-
terrupt request flag (TF) will be reset and the EMI bit
cleared to disable further interrupts.
During the execution of an interrupt subroutine, other in-
terrupt acknowledge signals are held until the RETI in-
struction is executed or the EMI bit and the related
interrupt control bit are set to 1 (if the stack is not full). To
return from the interrupt subroutine, RET or RETI
may be invoked. RETI will set the EMI bit to enable an
interrupt service, but RET will not.
Interrupts, occurring in the interval between the rising
edges of two consecutive T2 pulses, will be serviced on
the latter of the two T2 pulses, if the corresponding inter-
rupts are enabled. In the case of simultaneous requests
the following table shows the priority that is applied.
These can be masked by resetting the EMI bit.
Rev. 2.20
USB interrupt
Timer/Event Counter overflow
Access of the corresponding USB FIFO from PC
The USB suspend signal from PC
The USB resume signal from PC
USB Reset signal
Interrupt Source
Priority
1
2
Vector
0CH
04H
10
Once the interrupt request flags (TF, USBF) are set, they
will remain in the INTC register until the interrupts are ser-
viced or cleared by a software instruction. It is recom-
mended that a program does not use the CALL
subroutine within the interrupt subroutine. Interrupts of-
ten occur in an unpredictable manner or need to be ser-
viced immediately in some applications. If only one stack
is left and enabling the interrupt is not well controlled, the
original control sequence will be damaged once the
Oscillator Configuration
There is an oscillator circuit in the microcontroller.
This oscillator is designed for system clocks. The HALT
mode stops the system oscillator and ignores an exter-
nal signal to conserve power.
A crystal across OSC1 and OSC2 is needed to provide
the feedback and phase shift required for the oscillator.
No other external components are required. In stead of
a crystal, a resonator can also be connected between
OSC1 and OSC2 to get a frequency reference, but two
external capacitors in OSC1 and OSC2 are required.
The HT82M99E/HT82M99A can operate in 6MHz or
12MHz system clocks. In order to make sure that the
USB SIE functions properly, user should correctly con-
figure the SCLKSEL bit of the SCC Register. The default
system clock is 12MHz.
The WDT oscillator is a free running on-chip RC oscilla-
tor, and no external components are required. Even if
the system enters the power down mode, the system
clock is stopped, but the WDT oscillator still works within
a period of approximately 31 s. The WDT oscillator can
be disabled by ROM code option to conserve power.
Watchdog Timer - WDT
The WDT clock source is implemented by a dedicated
RC oscillator (WDT oscillator), or instruction clock (sys-
tem clock divided by 4), determine by ROM code option.
This timer is designed to prevent a software malfunction
or sequence from jumping to an unknown location with
unpredictable results. The Watchdog Timer can be dis-
abled by ROM code option. If the Watchdog Timer is dis-
abled, all the executions related to the WDT result in no
operation.
Once the internal WDT oscillator (RC oscillator with a
period of 31 s/5V normally) is selected, it is first divided
CALL operates in the interrupt subroutine.
System Oscillator
HT82M99E/HT82M99A
April 16, 2008