Programming Model

SCCIT<1:0>These bits define the IACK daisy chain time for the SCC chips. They must be set based on the number of SCC devices.

SCCIT<1:0>

Number of Z85230s

 

 

00

1

 

 

01

2

 

 

10

3

 

 

11

4

 

 

3

These bits must be initialized to 01 for the MVME172 boards

! because they contain two Z85230 devices.

Caution

Interrupt Vector Base Register

The interrupt vector base register is an 8-bit read/write register that is used to supply the vector to the MC68xx060 during interrupt acknowledge cycles. Only the most significant four bits are used. The least significant four bits encode the interrupt source during the acknowledge cycle.

The exception to this is that after reset occurs, the interrupt vector passed is $0f, which remains in effect until a write is generated to the vector base register.

A normal read access to the vector base register yields the value $0f if the read happens before it has been initialized. A normal read access yields all 0s on bits 0-3 and the value that was written on bits 4-7 if the read happens after the register has been initialized.

ADR/SIZ

 

 

 

$FFF42000 (8 bits)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

BIT

7

6

5

 

4

3

 

2

1

0

 

 

 

 

 

 

 

 

 

 

 

NAME

IV7

IV6

IV5

 

IV4

IV3

 

IV2

IV1

IV0

 

 

 

 

 

 

 

 

 

 

 

OPER

R/W

R/W

R/W

 

R/W

R

 

R

R

R

 

 

 

 

 

 

 

 

 

 

 

RESET

0 PL

0 PL

0 PL

 

0 PL

1 PL

 

1 PL

1 PL

1 PL

 

 

 

 

 

 

 

 

 

 

 

http://www.mcg.mot.com/literature

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Motorola MVME172 manual Interrupt Vector Base Register, SCCIT10 Number of Z85230s