Programming Model

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 last written on bits 4-7 if the read happens after the Vector Base Register has been initialized. A suggested setting of the Vector Base Register is $50.

ADR/SIZ

 

 

 

$FFF42003 (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

 

 

 

 

 

 

 

 

 

 

 

The encoding for the interrupt sources is shown below, where IV3-IV0 refer to bits 3-0 of the vector passed during the IACK cycle:

Interrupt Source

IV3-IV0

Priority

Printer Port-BSY

$0

Lowest

Printer Port-PE

$1

 

 

Printer Port-SELECT

$2

 

 

Printer Port-FAULT

$3

 

 

Printer Port-ACK

$4

 

 

SCSI IRQ

$5

 

 

LANC ERR

$6

 

 

LANC IRQ

$7

 

 

Tick Timer 2 IRQ

$8

 

 

Tick Timer 1 IRQ

$9

 

 

GPIO IRQ

$A

 

 

Serial Modem IRQ (auto vector mode only)

$B

 

 

Serial RX IRQ (auto vector mode only)

$C

 

 

 

 

Serial TX IRQ (auto vector mode only)

$D

Highest

The PCCchip2 supports an auto vector mode for the Cirrus Logic CD2401 SCC serial port. (Refer to the AVEC bit in the following registers: SCC Modem Interrupt Control Register, SCC Transmit Interrupt Control Register, and SCC Receive Interrupt Control Register.) If this mode is disabled by setting the AVEC bits to 0, then the PCCchip2 obtains the vector from the SCC and passes it to the MPU. Using the auto vector mode is NOT recommended.

3

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Page 215
Image 215
Motorola MVME1X7P manual Interrupt Source IV3-IV0 Priority, Gpio IRQ