20-668-0003 Rabbit Semiconductor, 20-668-0003 Datasheet - Page 49

• Manufacturer Part Number: 20-668-0003
• Description: IC CPU RABBIT2000 30MHZ 100PQFP
• Manufacturer: Rabbit Semiconductor

Specifications of 20-668-0003

• Processor Type: Rabbit 2000 8-Bit
• Speed: 30MHz
• Voltage: 2.7V, 3V, 3.3V, 5V
• Mounting Type: Surface Mount
• Package / Case: 100-MQFP, 100-PQFP
• Data Bus Width: 8 bit
• Maximum Clock Frequency: 30 MHz
• Operating Supply Voltage: 0 V to 5.5 V
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: - 40 C
• Number Of Programmable I/os: 40
• Number Of Timers: 8 & 10 bit
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Features: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: 20-668-0003; 316-1062

4.1.1 Pulse Width Modulation to Reduce Relay Power
Typically relays need far less current to hold them closed than is needed to initially close
them. For example, if the driver is switched to a 75% duty cycle using pulse width modu-
lation after the initial period when the relay armature is picked, the holding current will be
approximately 75% of the full duty-cycle current and the power consumption will be
about 56% as great.
The pulse width modulation rate may be from 5 kHz to 20 kHz. If a periodic interrupt is
established that interrupts every 50 µs, then a 50% duty cycle could be set up for a 100 µs
period. A 25%, 50% or 75% duty cycle could operate on a 200 µs period. A 250 µs period
would allow duty cycles of 20%, 40%, 60% or 80%. The code for such an interrupt routine
might appear as follows.
This routine would take approximately 15% of the processor’s compute time assuming
50 µs between interrupts. This routine could be speeded up, but at the expense becoming
more complicated. Instead of "and" and "or" masks, a higher level routine could modify
the array directly, and the end of the array could be detected by testing a bit pattern in HL.
The higher level routine would have to suppress the interrupt while changing the bit pat-
tern in the array, or otherwise prevent erratic outputs while the array is being changed. If
the relay emits a whistle at the period of the modulation, the acoustic energy can be spread
out over the spectrum by periodically missing an "off" pulse, creating a phase shift of
180°. A faster routine that executes in two-thirds the time is shown below.
Chapter 4 Rabbit Capabilities
push af
push hl
push de
ld hl,(ptr)
ld a,(maskand)
and a,(hl)
ld e,a
ld a,(maskor)
or a,e
ioi ld (port),a ; 13 store in port
inc hl
ld a,(hl)
or a,a
jr nz,step2
ld hl,(beginptr); 11 reset hl to start of array
step2:
ld (ptr),hl
pop de
pop hl
pop af
reti
; 153 clocks total worst case - 7.5 us at 20 MHz
; 10
; 11 get pointer to location in array
; 9 get mask
; 5 get current output
; 2
; 9
; 2
; 2 point to next
; 5 check for end of array
; 2
; 2
; 13 save hl
;7
; 7 return from interrupt
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