D950-CORE View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'D950-CORE' PDF : 89 Pages View PDF
D950-Core
Table 4.2 Interrupt Sources and Priority
RESET
SWI
INT
Sources
Non-Maskable
Non-Maskable
Maskable
Priority
Highest
Lowest
RESET
Non maskable (internally vectorized), either hardware or software (see Table 6.3.3“Hardware
Reset”)
In hardware, when a low level is applied to the RESET input, the CLOCK generator is re-
synchronized, the PC is reset, execution of NOP instructions is forced and control registers are
initialized.
In order to get a valid reset, a low level must be applied for a minimum of ten CLKIN cycles (i.e
five D950-Core cycles).
In software, the RESET instruction is a 3-cycle instruction having the same effects as a
hardware reset, except the CLOCK generator is not re-synchronized.
The reset address is 0x0000. By setting the MODE pin to 1, the alternate reset address
0XFC00 is selected.
INT
Maskable external interrupt EI and IPE bits of STA register (see Table 6.3.5“Interrupt”)
Start of Interrupt: External interrupt is disabled on reset and is enabled by setting EI-bit to 1.
As soon as an IT falling edge is memorized and recognized by the PCU at the beginning of an
instruction cycle, IPE-bit is set. Provided IT has been previously enabled, ITACK signal is
asserted low to acknowledge the interrupt. ITACK stays at the low state for one cycle, allowing
the interrupt vector to be provided by the controller on Y-bus. Then IPE-bit is reset. Interrupt
start processing requires three cycles to read the interrupt vector and to fetch the
corresponding instruction. Meanwhile, CCR register, STA and the return address are
automatically saved onto the stack, located in X-memory space.
Return from Interrupt: Return from the interrupt is performed by the RTI instruction, a 3-cycle
instruction during which the return address, STA register and CCR are retrieved from the
stack. The EOI signal is then asserted low, allowing the controller to arbitrate pending interrupt
requests and to issue, if required, the next interrupt request to the D950-Core.
An interrupt request that is recognized while decoding or executing a delayed branch
instruction, is not acknowledged until all operations related to the branch have been
completed.
In addition to this external interrupt source, a powerful interrupt controller is available as
peripheral of the D950-Core (see Section 7.3).
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