Remote-processing RPC-220 Instrukcja Użytkownika Pobierz pdf (Strona 13)

WRITING, DEBUGGING, AND SAVING PROGRAMS SECTION 3

Page 3-2

Figure 3-2 I/O and RAM Map

Code starting at 0x8000 should be exactly what you

would have if you were starting in EPROM at address 0,

except there is an 0x8000 offset. Interrupts are handled

by the monitor by jumping to 0x8000 + interrupt base.

Change your C compiler start up code so it starts at

0x8000. If you ordered the development system, then

the code needed to use the Dunfield compiler has been

included. Simply install the Dunfield compiler first, then

replace the files with those on the supplemental disk.

These files are 8051RLPT .ASM , 8051RL PM. ASM, and

8051RLPL.ASM.

The I/O map is more complicated because there are

more devices to select. All I/O is accessible regardless

of the setting of the development/normal mode bit.

Figure 3-2 is the external map.

Each area is selected by the following table:

Device/area Address

Flash EPROM 0x0000 - 0x7fff

Expansion port 0x8000 - 0x9fff

Real time clock (RTC) 0xa000 - 0xbfff

RAM segment 0xc000 - 0xffff

Several demonstration programs access I/O. Directories

where programs are located:

MEM 220

RTC

FLASH

ACCESSING I/O AND RAM

I/O devices and RAM share the same addresses. Access

to them is controlled by CPU port P4.0. When this line

is high, RAM is accessed using M OVX type commands.

When this line is low, the expansion port and real time

clock are accessed.

NOTE: The I/O contr ol line, CPU port P. 0, should be

low for as short a period of time as possible.

Additionally, interrupts should be turned off

while the line is low especially if the routine

accesses external memory. The following are

suggested steps to using the I/O port.

1 Set up pointers and registers as necessary to perform

the I/O operation.

2 Turn off interrupts (if used)

3 Set CPU port P4.0 low

4 Perform the read o r wr ite

5 Set CPU port 4.0 back high

6 Enable interrupts.

Step 4 above may consist of several reads and/or writes.

The idea is to keep this time short.

Alternately, you could write interrupt ser vice routines to

check the I/O line before accessing RAM. The line

would be r estored after servicing. The reason this

method is not recommended is the amount of time

needed to read, store, and restore the status is longer

than the time it takes to code straight through. If step is

4 long (say monitoring a clock status bit), perhaps the

extra overhead m ight be wor th it.

See the MEM220.C program to see how RAM and I/O

are accessed. Specialized speek and spoke functions are

written in assembly language. This wa s done not only to

speed up memory access and reduce interrupt off time

but to ensure correct access. N ote that parameters to the

function are passed in the stack and returned in registers

A and B. Make sure your compiler passes parameters

through the stack in the memory model you are using.

You may have to adjust parameter passing for your

compiler.

MONITOR ROM

The monitor ROM allows you to download code, set

breakpoints, examine and modify RAM and I/ O. T he

monitor occupies the same space as the final program

will. Generally, the final code replaces the

monitor when the project is done. The monitor can be

re-installed under two conditions:

1 Your code allows the flash to be written to. This is a

routine that must be included in your program. See

"SAVING YOUR PROGRAM TO FLASH".

2 The flash is removed from the socket and

programmed using an external programmer.

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