HT82K95E Datasheet, PDF (10/48 Pages) Holtek Semiconductor Inc – USB Multimedia Keyboard Encoder 8-Bit MCU

HT82K95E/HT82K95A
In addition, on entering the interrupt sequence or exe-
cuting the subroutine call, the status register will not be
pushed onto the stack automatically. If the contents of
the status are important and if the subroutine can cor-
rupt the status register, precautions must be taken to
save it properly.
Interrupt
The device provides an external interrupt and internal
timer/event counter interrupts. The Interrupt Control
Register (INTC;0BH) contains the interrupt control bits
to set the enable/disable and the interrupt request flags.
Once an interrupt subroutine is serviced, all the other in-
terrupts will be blocked (by clearing the EMI bit). This
scheme may prevent any further interrupt nesting. Other
interrupt requests may occur during this interval but only
the interrupt request flag is recorded. If a certain inter-
rupt requires servicing within the service routine, the
EMI bit and the corresponding bit of the INTC may be set
to allow interrupt nesting. If the stack is full, the interrupt
request will not be acknowledged, even if the related in-
terrupt is enabled, until the SP is decremented. If immedi-
ate service is desired, the stack must be prevented from
becoming full.
All these kinds of interrupts have a wake-up capability.
As an interrupt is serviced, a control transfer occurs by
pushing the program counter onto the stack, followed by
a branch to a subroutine at specified location in the pro-
gram memory. Only the program counter is pushed onto
the stack. If the contents of the register or status register
(STATUS) are altered by the interrupt service program
which corrupts the desired control sequence, the con-
tents should be saved in advance.
USB interrupts are triggered by the following USB
events and the related interrupt request flag (USBF; bit
4 of the INTC) will be set.
· The corresponding USB FIFO is accessed from the
PC
· The USB suspends signal from the PC
· The USB resumes signal from the PC
· The USB sends Reset signal
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 HT82K95E/
HT82K95A, 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 HT82K95E/HT82K95A receives a
USB Suspend signal from the Host PC, the suspend line
(bit0 of the USC) of the HT82K95E/HT82K95A is set
and a USB interrupt is also triggered.
Also when the HT82K95E/HT82K95A receives a Re-
sume signal from the Host PC, the resume line (bit3 of
the USC) of HT82K95E/HT82K95A is set and a USB in-
terrupt is triggered.
Whenever a USB reset signal is detected, the USB in-
terrupt is triggered.
The internal Timer/Event Counter 0 interrupt is initial-
ized by setting the Timer/Event Counter 0 interrupt re-
quest flag (; bit 5 of INTC), caused by a timer 0 overflow.
When the interrupt is enabled, the stack is not full and
the T0F bit is set, a subroutine call to location 08H will
occur. The related interrupt request flag (T0F) will be re-
set and the EMI bit cleared to disable further interrupts.
The internal Timer/Even Counter 1 interrupt is initialized
by setting the Timer/Event Counter 1 interrupt request
flag (;bit 6 of INTC), caused by a timer 1 overflow. When
the interrupt is enabled, the stack is not full and the T1F
is set, a subroutine call to location 0CH will occur. The
related interrupt request flag (T1F) 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 ²RETI² in-
struction is executed or the EMI bit and the related
interrupt control bit are set to ²1² (if the stack is not full).
To return from the interrupt subroutine, ²RET² or ²RETI²
may be invoked. RETI will set the EMI bit to enable an in-
terrupt service, but RET will not.
Bit No.
0
1
2
3
4
5
6
7
Label
EMI
EUI
ET0I
ET1I
USBF
T0F
T1F
¾
Function
Controls the master (global) interrupt (1= enabled; 0= disabled)
Controls the USB interrupt (1= enabled; 0= disabled)
Controls the Timer/Event Counter 0 interrupt (1= enabled; 0= disabled)
Controls the Timer/Event Counter 1 interrupt (1= enabled; 0= disabled)
USB interrupt request flag (1= active; 0= inactive)
Internal Timer/Event Counter 0 request flag (1= active; 0= inactive)
Internal Timer/Event Counter 1 request flag (1= active; 0= inactive)
Unused bit, read as ²0²
INTC (0BH) Register
Rev. 1.20
10
October 24, 2005