Look-Up Table Registers - Tblp, Tblh; Status Register - Status - Holtek HT46R47 Handbook

Look-up Table Registers - TBLP, TBLH

These two special function registers are used to control operation of the look-up table which is
stored in the Program Memory. TBLP is the table pointer and indicates the location where the table
is located. Its value must be setup before any table read commands are executed. Its value can be
changed, for example using the INC or DEC instructions, allowing for easy table data pointing and
reading. TBLH is the location where the high order byte of the table data is stored after a table read
data instruction has been executed. Note that the lower order table data byte is transferred to a
user defined location.

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 (PDF), and watchdog time-out flag (TO). It also records the status infor-
mation and controls the operation sequence.
With the exception of the TO and PDF flags, bits in the status register can be altered by in-
structions like most other registers. Any data written into the status register will not change
the TO or PDF flag. In addition, operations related to the status register may give different re-
sults due to the different instruction operations. The TO flag can be affected only by a system
power-up, a WDT time-out or by executing the ²CLR WDT² or ²HALT² instruction. The PDF
flag is affected only by executing the ²HALT² or ²CLR WDT² instruction or during a system
power-up.
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 addition operation or if a borrow 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 an 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 logical operation is zero; otherwise Z is cleared.
· OV is set if an operation results in a carry into the highest-order bit but not a carry out of the high-
est-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 ex-
ecuting 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.
Chapter 1 Hardware Structure
S T A T U S R e g i s t e r
A r i t h m e t i c / l o g i c o p e r a t i o n f l a g s
S y s t e m m a n a g e m e n t f l a g s
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