SDA5250 Datasheet, PDF (75/143 Pages) Siemens Semiconductor Group – TVTEXT 8-Bit Microcontroller

SDA 525x
Table 19
Instruction
Time (Oscillator Periods)
Best Case
Worst Case
External interrupt generated immediately
before (best) / after (worst) the pin is
2+ε
sampled (time until end of bus cycle).
[1 + ε] 2 – ε
[1 – ε]
Current or next instruction finishes in 12
[6]
12
[6]
12-[6-] oscillator periods
Next instruction is MUL or DIV
don’t care
48
[24]
Internal latency for hardware subroutine 24
[12]
24
[12]
call
38
[19]
86
[43]
Note: values without brackets apply for CDC = 1 and values in brackets for CDC = 0
(see Chapter “Advanced Function Register” on page 115).
If an interrupt of equal or higher priority level is already in progress, the additional wait
time obviously depends on the nature of the other interrupt's service routine.
6.3.5
Processor Reset and Initialization
Processor initialization is accomplished with activation of the RST pin, which is the input
to a Schmitt Trigger. To reset the processor, this pin should be held low for at least four
machine cycles, while the oscillator is running stable. Upon powering up, RST should be
held low for at least 10 ms after the power supply stabilizes to allow the oscillator to
stabilize. Crystal operation below 6 MHz will increase the time necessary to hold RST
low. Two machine cycles after receiving of RST, the processor ceases from instruction
execution and remains dormant for the duration of the pulse. The high-going transition
then initiates a sequence which requires approximately one machine cycle to execute
before normal operation commences with the instruction at absolute location 0000_H.
Program memory locations 0000_H through 0002_H are reserved for the initialization
routine of the microcomputer. This sequence ends with registers initialized as shown in
Chapter “Memory Organization” on page 49.
After the processor is reset, all ports are written with one (1). Outputs are undefined until
the reset period is complete.
An automatic reset can be obtained when V_DD is turned on by connecting the RST-pin to
V_SS through a 10 µF capacitor, providing the V_DD rise time does not exceed a millisecond
and the oscillator start-up time does not exceed 10 milliseconds. When power comes on,
the current drawn by RST-pin starts to charge the capacitor. The voltage V_RST at RST-pin
is the capacitor voltage, and increases to V_DD as the capacitor charges. The larger the
Semiconductor Group
75
1998-04-08