Symbol
Parameter
Test Conditions
Min. Typ. Max. Unit
V
DD
Conditions
t
WDT2
Watchdog Time-out Period
(System Clock)
Without WDT
prescaler
1024
t
SYS
t
WDT3
Watchdog Time-out Period
(RTC OSC)
Without WDT
prescaler
7.812
ms
t
RES
External Reset Low Pulse
Width
1
s
t
SST
System Start-up Timer
Period
Power-up, reset or
wake-up from HALT
1024
t
SYS
t
INT
Interrupt Pulse Width
1
s
Functional Description
HT48C50-1
7
June 14, 2000
Preliminary
Execution flow
The system clock for the microcontroller is de-
rived from either a crystal or an RC oscillator.
The system clock is internally divided into four
non-overlapping clocks. One instruction cycle
consists of four system clock cycles.
Instruction fetching and execution are
pipelined in such a way that a fetch takes an in-
struction cycle while decoding and execution
takes the next instruction cycle. However, the
pipelining scheme causes each instruction to ef-
fectively execute in a cycle. If an instruction
changes the program counter, two cycles are re-
quired to complete the instruction.
Program counter
PC
The program counter (PC) controls the se-
quence in which the instructions stored in the
program ROM are executed and its contents
specify a full range of program memory.
After accessing a program memory word to fetch
an instruction code, the contents of the program
counter are incremented by one. The program
counter then points to the memory word contain-
ing the next instruction code.
When executing a jump instruction, conditional
skip execution, loading PCL register, subrou-
tine call, initial reset, internal interrupt, exter-
nal interrupt or return from subroutine, the PC
manipulates the program transfer by loading
the address corresponding to each instruction.
The conditional skip is activated by instruc-
tions. Once the condition is met, the next in-
struction, fetched during the current
instruction execution, is discarded and a
dummy cycle replaces it to get the proper in-
struction. Otherwise proceed with the next in-
struction.
1
+
1
+
1
+
9 ! ) *
* 6
8
: ! * * 6 ; 8
9 ! ) *
* 6
< 8
: ! * * 6 8
9 ! ) *
* 6
< 8
: ! * * 6 < 8
<
<
& ! * =
* 6 * & 8
Execution flow