HT82B40R_14 Datasheet, PDF (13/54 Pages) Holtek Semiconductor Inc – I/O 8-Bit MCU with USB Interface

HT82B40R/HT82B40A
b7
b0
T O P D F O V Z A C C S T A T U S R e g is te r
A r ith m e tic /L o g ic O
C a r r y fla g
A u x ilia r y c a r r y fla g
Z e r o fla g
O v e r flo w fla g
p e r a tio n
F la g s
S y s te m M a n a g e m e n t F la g s
P o w e r d o w n fla g
W a tc h d o g tim e - o u t fla g
N o t im p le m e n te d , r e a d a s " 0 "
Status Register
The Z, OV, AC and C flags generally reflect the status of
the latest operations.
· C is set if an operation results in a carry during an ad-
dition operation or if a borrow does not take place dur-
ing a subtraction operation; otherwise C is cleared. C
is also affected by a rotate through carry instruction.
· AC is set if an operation results in a carry out of the
low nibbles in addition, or no borrow from the high nib-
ble into the low nibble in subtraction; otherwise AC is
cleared.
· Z is set if the result of an arithmetic or logical operation
is zero; otherwise Z is cleared.
· OV is set if an operation results in a carry into the high-
est-order bit but not a carry out of the highest-order bit,
or vice versa; otherwise OV is cleared.
· PDF is cleared by a system power-up or executing the
²CLR WDT² instruction. PDF is set by executing the
²HALT² instruction.
· TO is cleared by a system power-up or executing the
²CLR WDT² or ²HALT² instruction. TO is set by a
WDT time-out.
In addition, on entering an interrupt sequence or execut-
ing a subroutine call, the status register will not be
pushed onto the stack automatically. If the contents of
the status registers are important and if the interrupt rou-
tine can change the status register, precautions must be
taken to correctly save it.
Interrupt Control Registers - INTC
The microcontrollers provide two internal timer/event
counter overflow interrupts and one USB interrupt. By
setting various bits within this register using standard bit
manipulation instructions, the enable/disable function of
each interrupt can be independently controlled. A mas-
ter interrupt bit within this register, the EMI bit, acts like a
global enable/disable and is used to set all of the inter-
rupt enable bits on or off. This bit is cleared when an in-
terrupt routine is entered to disable further interrupt and
is set by executing the ²RETI² instruction.
Timer/Event Counter Registers -
TMR0, TMR0C, TMR1H, TMR1L, TMR1C
Both devices possess a single internal 8-bit count-up
timer. An associated register known as TMR0 is the lo-
cation where the timers 8-bit value is located. This regis-
ter can also be preloaded with fixed data to allow
different time intervals to be setup. An associated con-
trol register, known as TMR0C, contains the setup infor-
mation for this timer, which determines in what mode the
timer is to be used as well as containing the timer on/off
control function.
All devices possess one internal 16-bit count-up timer.
An associated register pair known as TMR1L/TMR1H is
the location where the timer 16-bit value is located. This
register can also be preloaded with fixed data to allow
different time intervals to be setup. An associated con-
trol register, known as TMR1C, contains the setup infor-
mation for this timer, which determines in what mode the
timer is to be used as well as containing the timer on/off
control function.
Input/Output Ports and Control Registers
Within the area of Special Function Registers, the I/O
registers and and their associated control registers play
a prominent role. All I/O ports have a designated regis-
ter correspondingly labeled as PA, PB, PC, PD and
PE0~PE1. These labeled I/O registers are mapped to
specific addresses within the Data Memory as shown in
the Data Memory table, which are used to transfer the
appropriate output or input data on that port. With each
I/O port there is an associated control register labeled
PAC, PBC, PCC, PDC and PEC, also mapped to spe-
cific addresses with the Data Memory.
The control register specifies which pins of that port are
set as inputs and which are set as outputs. To setup a
pin as an input, the corresponding bit of the control reg-
ister must be set high, for an output it must be set low.
During program initialisation, it is important to first setup
the control registers to specify which pins are outputs
and which are inputs before reading data from or writing
data to the I/O ports. One flexible feature of these regis-
ters is the ability to directly program single bits using the
Rev. 1.70
13
November 5, 2014