Motorola M68CPU32BUG Manual de usuario descargar pdf (Pagina 36)

MOTOROLA MC68332TUT/D

states. If a chip-select circuit is used to provide an autovector, fast termination is automatically

selected, and the DSACK field is not used. For more information on how to determine the number

of wait states needed, see 2.9.1 Using Chip-Selects to Generate DSACK

F. SPACE — This field indicates the address space of the access. To access memory, select super-

visor/user space. For IACK cycles, select CPU space.

G. IPL — If the chip-select circuit is used to provide an IACK signal or AVEC, the IPL field indicates

the interrupt priority level selected.

H. AVEC — This field determines whether a chip-select circuit generates an autovector in response

to an IACK initiated by the assertion of an IRQ pin. For normal bus cycles, this field is not used. If

a chip-select circuit is to be used to generate an IACK signal, program this field to zero to disable

autovector generation. If a chip-select is to be used to generate an autovector, program this field

to one.

4.2.9 General-Purpose I/O Ports

Certain SIM pins can be configured as general-purpose I/O ports when not used for other purposes. Port E

pins share function with bus-control signals, port F pins share function with interrupt request signals, and

port C (output only) pins share functions with chip-select signals. The ports are controlled by pin assignment

registers (CSPAR, PEPAR, and PFPAR) and data direction registers (DDRE and DDRF). Pin assignment

registers determine whether a pin is used for general-purpose I/O or for another function. Data direction reg-

isters determine whether an I/O pin is an input or an output. Data is written to and read from the port data

registers (PORTC, PORTE and PORTF).

1. Assign port pins by writing to pin assignment registers.

2. Program the data direction registers to assign input or output function to port pins

3. Use the port data registers to read/write data.

4.2.10 Example of SIM Initialization

This example assumes that two other files, org00000.asm and org00008.asm, exist. The file org00000.asm

initializes the stack pointer and program counter. It contains the code shown in 4.1.3.1 Initializing the Re-

set Vector. The file org00008.asm initializes the interrupt vectors. It contains the code shown in 4.1.3.2 Ini-

tializing Exception Vectors other than Reset. This file is not necessary for debugging, but should be

included in final application code. The code can be assembled with the IASM32 assembler.

CSBARBT EQU $FFFA48

CSBAR0 EQU $FFFA4C

CSBAR1 EQU $FFFA50

CSBAR2 EQU $FFFA54

CSORBT EQU $FFFA4A

CSOR0 EQU $FFFA4E

CSOR1 EQU $FFFA52

CSOR2 EQU $FFFA56

CSPAR0 EQU $FFFA44

PICR EQU $FFFA22

PITR EQU $FFFA24

SYNCR EQU $FFFA04

SYPCR EQU $FFFA21

SIMCR EQU $FFFA00

* INCLUDE 'org00000.asm' ;include reset vector

* INCLUDE 'org00008.asm' ;include other exception vectors

ORG $400 ;begin program at $400, immediately after

;the exception table

CLR.L D0

MOVEC D0,VBR ;make sure that VBR is initialized to zero

;it is initialized to 0 out of reset

INITSYS:

1 2 ... 31 32 33 34 35 36 37 38 39 40 41 ... 55 56

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Motorola M68CPU32BUG Manual de usuario Pagina 36

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