45300 Parallax Inc, 45300 Datasheet - Page 102
45300
Manufacturer Part Number
45300
Description
BOARD PROTO SX48
Manufacturer
Parallax Inc
Type
MCUr
Specifications of 45300
Contents
Board
Lead Free Status / RoHS Status
Contains lead / RoHS non-compliant
For Use With/related Products
SX48
For Use With
130-28029 - KIT PARTS SMART SENSORS45111 - MANUAL FOR SX-KEY/BLITZ VER. 2.028850 - CARRIER BOARD BOARD OF EDU USB
Lead Free Status / RoHS Status
Lead free / RoHS Compliant, Contains lead / RoHS non-compliant
Available stocks
Company
Part Number
Manufacturer
Quantity
Price
Part Number:
453001
Manufacturer:
LITTELFUSE/力特
Quantity:
20 000
Company:
Part Number:
453002
Manufacturer:
LITTELFU
Quantity:
1 000
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10 SX Special Features and Coding Tips
By adjusting the value in W before the RETIW command, various amounts of cycle bandwidth will be
allocated to the main routines. Normally this won’t be a problem but care should be taken to ensure that
the RTCC doesn’t rollover too often, causing little or no cycle time to be allocated to the main routines.
If the RTCC adjustment value is too small for the size of the interrupt routine, the main routine may
eventually hang up, may not execute at all, or the interrupt routine will miss the rollover and only
execute every 256 cycles. Use the following equation as a general rule-of-thumb when determining the
minimum adjustment value:
Minimum RTCC Adjustment Value = -(max cycles for interrupt + 6)
The 6 in this equation accounts for the number of cycles required to enter the interrupt routine (3 cycles)
plus the number of additional cycles needed to complete the longest command (3 cycles extra to finish
an IREAD). If the IREAD command is not used in the main program, a value of -(maximum cycles for
interrupt + 4) is the minimum, allowing for only a single instruction in the main routine to be executed
between interrupts.
As an example, the following interrupt routine takes 4 cycles to execute:
Interrupt
The adjustment value of –8, which is –(max cycles for interrupt + 4), will cause the interrupt routine to
execute every 8 cycles and will only allow one single-cycle or one three-cycle instruction in the main
routine to execute between interrupts. If the main routine contained an IREAD command, however, the
main routine would execute one instruction between interrupts until it reached the IREAD, at which
point it would get eternally stuck, and only the interrupt would continue. As another example, if the
adjustment value was –7, this would be too small an adjustment and would cause the interrupt routine
to execute, but no instructions in the main routine would execute at all.
Page 102 SX-Key/Blitz Development System Manual 2.0 Parallax, Inc.
MOV
RETIW
1) RTCC rolls over
2) 3 cycles required to enter interrupt routine
3) Interrupt routine executes
4) –50 (206 in twos-compliment) is added to RTCC
5) RTCC rolls over again in exactly 19 additional
cycles (Path 1) or 32 additional cycles (Path 2)
W, #-8
Event
; 1 cycle
; 3 cycles
Table 21 - Interrupt Timing
Total Cycles = 31 + 19 =
(28 cycles)
RTCC = 237
RTCC = 31
RTCC = 0
RTCC = 3
Path 1
50
Total Cycles = 18 + 32 =
(15 cycles)
RTCC = 224
RTCC = 18
RTCC = 0
RTCC = 3
Path 2
50
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