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DATA MEMORY CHAPTER 5

Page 12 RPC-150

Figure 5-1 Data memory

INTRODUCTION

The RP C-150 is available with 32 of RAM . RAM is in

socket U1. RA M may be battery backed by installing a

DS-1213C in socket U1. RAM is installed on top of U1.

Battery life depends upon RAM power consum ption,

temperature, and amount of time the board is operating.

Generally, a battery life from 5 to 10 years can be

expected.

This chapter discusses installing a battery backup for

RAM, saving and retrieving variables, and running

assembly language programs. Figure 5-1 shows the

location of U1.

If program and data are battery backed, the UNNEW

command may be used to restore the program.

Variables used by the Basic program are cleared,

however. Data POKEd into RAM is saved.

BATTERY BACKUP

A Dallas Semiconductor DS-1213C is used to battery

backup RAM when power is off. Battery life depends

upon RAM size, type, and time the RPC-150 has power

applied to it. You can expect the battery to last between

5 to 10 years at 25°C. Battery life decreases by 1/2 at

50°C.

To install a DS-1213C, r emove the RAM chip in U1,

install the DS-1213C, and install the RAM chip on top of

the module.

STORING VARIABLES IN RAM

The term "var iables" in this context includes numb ers,

strings, arrays, recipes, and formulas as applied to your

application.

Program s, CA MBASIC variables, and variables you

POKE and P EEK to are fr om 8000H to FF FFH . The

program and b asic numb er variables (A, B(15), ect.)

are ' on top' of the program and are cleared on reset.

String variables (e.g. c$) are below the stack. The stack

requires 255 bytes and string space will depend upon

how much you CLEARed on power up. If you do not

use the CLEAR statement, assume 500 bytes are

available for strings. Data you peek and poke to must be

between the end of num ber variables and start of strings.

The procedure to determ ine the 'safe' area to Poke

variables follows. First, download and run your

program. What you want to do is for ce the basic to

allocate space for most all of the variables in your

program. Next, exit your program and perform a

PRIN T SYS(2), SYS(1) in the immediate mode. T his

will print out the address for the bottom of the stack and

top of the program with variables. Subtract the number

used in your CLEAR statement from the first number

printed. If you did not use the CLEAR statement,

subtract 500. In case your progr am did not execute

completely, you may w ant to add 500 to the second

number. This range is where you can PO KE to.

Many times you will start with a very small program and

add to it. In this case the above procedure is not

adequate. The best w ay to handle this situation is to

figure out the number of bytes used for string variables

in the program. This determined by the CLEAR

statement. If you do not use the CLEAR statement, then

you can figure the bottom of the stack and string space

start at address 0FD00H. When you start using POKE

statements, assign new variables BELOW this address.

To put it another way, count down and not up as you add

POKE locations. Remember when using string and

floating point POKEs the address specified is the starting

address and will go up.

PEEK and POKE commands store and retrieve values

from memory. For example:

20 POKE 60000, A

puts the value of A into address 60000.

Use the PEEK statement to retrieve the variable:

1 2 ... 9 10 11 12 13 14 15 16 17 18 19 ... 25 26

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