668-0003-C Rabbit Semiconductor, 668-0003-C Datasheet - Page 50

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

Specifications of 668-0003-C

• Rohs Status: RoHS non-compliant
• 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
• Features: -
• Other names: 316-1004; 668-0003

4.2 Open-Drain Outputs Used for Key Scan
The parallel port D outputs can be individually programmed to be open drain. This is use-
ful for scanning a switch matrix, as shown in Figure 4-2. A row is driven low, then the col-
umns are scanned for a low input line, which indicates a key is closed. This is repeated for
each row. The advantage of using open-drain outputs is that if two keys in the same col-
umn are depressed, there will not be a fight between a driver driving the line high and
another driver driving it low.
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push af
push hl
ld hl,(ptr)
ld a,(hl)
ioi ld (port),a ; 13 output data
inc hl
ld a,0x0f
and l
jr z,step2
ld (ptr),hl
pop hl
pop af
reti
step2:
ld a,(beginptr)
ld l,a
ld (ptr),hl
pop hl
pop af
reti
; 103 clocks total
o.d.
o.d.
Figure 4-2. Using Open-Drain Outputs for Key Scan
;10
;11
;5
;4
; see if hl at end of cycle
;13
;7
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Rabbit 2000 Microprocessor User’s Manual
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