Remote-processing RPC-220 Instrukcja Użytkownika Pobierz pdf (Strona 23)

RAM SECTION 5

Page 5-1

RAM SECTION 5

This section discusses accessing RAM and battery

backup.

ACCESSING RAM

RAM is accessed using MOVX type instructions. The

I/O control bit (C PU port P4.0) m ust be high. This bit

is high on power up or reset.

The 8051 series of C PU' s access RA M 64K bytes at a

time. Additional RAM is accessed using a bank

selection scheme. Bank selection in the RPC -220 is

done by writing to an I/O addr ess.

Demonstration program MEM220.C accesses all RAM

segments. Byte and word wide accesses are through

functions speek, spoke, speekw, and spokew.

On power up or reset, RAM segment is set to 0. To

change the RAM segment, do an I/O write to addr ess

0xcYzz

Where:

0xc is the constant part of the address

Y determines the segm ent selected ac cording to

the formula below.

zz is don't care data.

Simply writing to this addr ess sets the segm ent. No data

is involved. Use the following formula to calculate the

address based on the segment desired:

address = 0xc000 + segment * 0x800

The best w ay is in assembly language. T his is shown in

the speek and spoke type routines in MEM220. C under

the ME M220 director y. E ssentially, DPH is loaded with

the address after shifting (multiplying) the segment.

You can use either compiler supplied peek and poke

functions or a pointer to access RAM in segment 0. Use

caution when using these functions to access other

segments. Normally, C stores variables in segment 0.

If you have code like:

CLR P4.0 // set I/O mode

poke(addr1,value1); // set segment

SETB P4.0 // Back to RAM mode

poke(addr2,value2); // Save memory

All of the variables, unless they are register, are bogus

since they were obtained from the wrong segment in

RAM.

WARNING:

Turn off interrupts befor e accessing R AM in

segments 1-7 unless you make your handlers switch

to segment 0. You can use seriously wrong

variables if the progr am assum es they are in

segment 0 and you are working another segment 1.

WARNING:

When you are logging data and are in the

development mode, you can easily modify the code

in segment 0. Code starts at 0x8000. Start logging

data in segment 1.

BATTERY BACKUP

The RPC-220 comes in two versions with battery backed

RAM. Battery backup is controlled by the RTC chip U8.

The supplied battery can expect to back up RAM and

keep the clock going for about 4-6 years with a 128K

RAM, the unit completely off, and sitting at 25°C.

Battery life degrades quickly, about 50%, at 50°C. You

can extend battery back up life by installing your own.

See SECTION 7, EXTERNAL BATTERY, for more

information.

RAM SIZE JUMPER

Jumper W1 configures RAM U4 for 128K or 512K. It is

preset at the factory.

APPLICATION PROGRAMS

The following programs are in the MEM 220 directory.

File name Description

MEM220.C Extended memory access routines.

MEMTST22.C A slow, but extensive m emor y test.

All 512K RAM checked. Prim arily to

check for overlapping memory

segments.

1 2 ... 18 19 20 21 22 23 24 25 26 27 28 ... 46 47

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