ST9 datasheet(43/146 Pages) STMICROELECTRONICS

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ST9 USER GUIDE

Figure 15

. Interrupt Vectors

As an example, let’s take the ST92F150 Multifunction Timer 0. The registers that define the

MFT0 functions are all contained in pages 9 and 10 of register group 15 (0FH). Register 242,

called the Interrupt Vector Register (IVR), holds the address of the beginning of the vector

array in program memory. The IVR has the following bit layout:

00 0000

00 FFFF

01 0000

XX FFFF

ISR 0000

R240

R255

Paged Registers

Interrupt Vector

Interrupt Service

Routine Address

8-bit

Memory Space

Interrupt Program

6-bit

8-bit

22-bit

16-bit

ISR

Segment

22-bit

Bit D0 of IVR is always 0

since the addresses of the

interrupt service routine

start at even addresses

Divide by Zero Trap

ISR Address of

Divide by Zero Trap

ISR Address of

RESET

ISR Address of

repeated at each

segment

Only for the first

segment

00 0002

ISR 0002

At the end of the Interrupt Service

Routine, the IRET instruction returns

to the program in the segment

selected by CSR (CSR_5 to CSR_0)

PC from stack

22-bit

Divide by zero trap

(1) If the ENCSR bit of EMR2 is set (Enable Code Segment Register), the CSR is saved in the stack and then

CSR from stack

ISR

CSR

(2)

loaded by the ISR. If it’s reset, the CSR is not saved and only the ISR is used.

(2) If the ENCSR is set, the CSR is reloaded with the value saved in the stack when the interrupt occurs.

If it’s reset, CSR is used instead of ISR when the RETI instruction occurs (Return from interrupt).

ISR or CSR(1)

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