HTG2150 datasheet(13/49 Pages) HOLTEK

13 / 49 page

HTG2150

July 24, 2000

Preliminary

Arithmetic and logic unit - ALU

This circuit performs 8-bit arithmetic and logic

operation. The ALU provides the following

functions:

· Arithmetic operations (ADD, ADC, SUB,

SBC, DAA)

· Logic operations (AND, OR, XOR, CPL)

· Rotation (RL, RR, RLC, RRC)

· Increment and Decrement (INC, DEC)

· Branch decision (SZ, SNZ, SIZ, SDZ ....)

The ALU not only saves the results of a data op-

eration but also changes the status register.

Status register - STATUS

This 8-bit register (0AH) contains the zero flag

(Z), carry flag (C), auxiliary carry flag (AC),

overflow flag (OV), power down flag (PD) and

watchdog time-out flag (TO). It also records the

status information and controls the operation se-

quence.

With the exception of the TO and PD flags, bits

in the status register can be altered by instruc-

tions like any other register. Any data written

into the status register will not change the TO

or PD flags. In addition it should be noted that

operations related to the status register may

give different results from those intended. The

TO and PD flags can only be changed by system

power up, Watchdog Timer overflow, executing

the HALT instruction and clearing the Watch-

dog Timer.

The Z, OV, AC and C flags generally reflect the

status of the latest operations.

In addition, on entering the interrupt sequence

or executing the subroutine call, the status reg-

ister will not be automatically pushed onto the

stack. If the contents of status are important

and if the subroutine can corrupt the status

properly.

Interrupt

The HTG2150 provides an external interrupt and

a PWM D/A interrupt and internal timer inter-

rupts. The Interrupt Control register (INTC;0BH,

INTCH;1EH) contains the interrupt control bits to

set the enable/disable and the interrupt request

flags.

Once an interrupt subroutine is serviced, all

other interrupts will be blocked (by clearing the

EMI bit). This scheme may prevent any further

interrupt nesting. Other interrupt requests may

happen during this interval but only the inter-

Labels

Bits

Function

C is set if the operation results in a carry during an addition operation or if a bor-

row does not take place during a subtraction operation; otherwise C is cleared. C

is also affected by a rotate through carry instruction.

AC is set if the operation results in a carry out of the low nibbles in addition or no

borrow from the high nibble into the low nibble in subtraction; otherwise AC is

cleared.

Z is set if the result of an arithmetic or logic operation is zero; otherwise Z is

cleared.

OV is set if the operation results in a carry into the highest-order bit but not a

carry out of the highest-order bit, or vice versa; otherwise OV is cleared.

PD is cleared when either a system powers up or a CLR WDT instruction is exe-

cuted. PD is set by executing the HALT instruction.

TO is cleared by a system power-up or executing the CLR WDT or HALT in-

struction. TO is set by a WDT time-out.

6, 7

Undefined bits, read as ²0².

Status register

HTG2150 Datasheet(PDF) 13 Page - Holtek Semiconductor Inc

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