
EZ-USB FX2 Technical Reference Manual
Page 4-22 EZ-USB FX2 Technical Reference Manual v2.1
Figure 4-7. The FIFO/GPIF Autovector Mechanism in Action
Figure 4-7 illustrates an ISR that services EP4’s Full Flag. When EP4 goes full, the FX2 asserts
the FIFO/GPIF interrupt request, vectoring to location 0x0053.
The jump instruction at this location, which was originally coded as “LJMP 0480”, becomes “LJMP
04A4” because the FX2 automatically inserts A4, the INT4VEC value for EP4FF (Table 4-13).
The FX2 jumps to 0x04A4, where it executes the jump instruction to the EP4FF ISR, arbitrarily
located for this example at address 0x0321.
Once the FX2 vectors to 0x0053, initiation of the endpoint-specific ISR takes only eight instruction
cycles.
EP4FF_ISR
FIFO_GPIF_Jmp_Table:
LJMP
04
A4
0x0053
0x0054
0x0055
A4
INT4VEC
Automatically
copied by FX2
LJMP EP4FF_ISR
01
19
0x04A4
0x04A5
0x04A6
0x0480
0x0321
FIFO/GPIF
Interrupt
Vector
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