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It can bee seen that MASTER_ENABLE is a combinational signal. Lets look at the L15D's inputs. These signals are the inverted Q output of a dual Flip-Flop. These are simply single state status registers that reflect the power conditions. Since the inverted outputs are used the default state of the status register is logical 1. Any time a fault condition exists these bits will be cleared. This makes a false MASTER_ENABLE signal which effectively disables the fuel injectors. TTL_FUEL_DELIVERY and L8_P29 must also be true for MASTER_ENABLE to be true. L8_P29 is likely to be output compare mode, which would limit the pulse-width of the TTL_FUEL_DELIVERY signal.
<<Go Back to Chip Location Reference
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L15, 74HC08 Quad 2-input AND gate |
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Pin # |
Pin Description |
Circuit Configuration |
IDM Function |
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1 |
Gate #1 input |
Fuel Delivery Input possible open coll |
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2 |
Gate #1 input |
Driven by (L8-P29) |
Fuel Delivery Valid |
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3 |
Gate #1 output |
Drives (L15-P4) |
Valid Fuel Delivery Pulse Enable out |
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4 |
Gate #2 input |
Driven by (L15-P3) |
Valid Fuel Delivery |
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5 |
Gate #2 input |
Driven by (L15-P11) |
(/Q1 & /Q2) result |
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6 |
Gate #2 output |
Drives (L1-P1,4,9,12) (L2-P1,4,9,12) |
Master Enable Output |
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7 |
GND |
Common GND |
Power GND for device |
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8 |
Gate #3 output |
Drives (L6-P9) |
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9 |
Gate #3 input |
Fuel Delivery Input |
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10 |
Gate #3 input |
Driven by (L8-P10) |
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11 |
Gate #4 output |
(/Q1 & /Q2) result |
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12 |
Gate #4 input |
Driven by (L17-P6) |
/Q1 output from Flip-Flop |
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13 |
Gate #4 input |
Driven by (L17-P8) |
/Q2 output from Flip-Flop |
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14 |
VCC |
Common 5VDC |
Power 5VDC for device |