tcj_08 1984-06 02.04.pdf

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THE COMPUTER JOURNAL

For Those Who Interface, Build, and Apply Micros

Vol II, No 4

$2,50

Build a VIC-20 EPROM Programmer

Multi-user:

CP/NET

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plllel

Build a High-Resolution 5-100

Graphics Board

Part Three:Construction

pllge 10

System Integration

Part Three: CP/M 3.0

pllle 17

Linear Optimization with Micros

LSTTL Reference Chart

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pllle2S

Editor's Page

The Customer is Tired of Being Ignored!

Many of the companies in the microcomputer

industry have developed a very simple customer

relations

policy - they

just

ignore

correspondence and phone calls. This may have

been a cost-effective way of handling the problem

in an expanding market filled with eager and

unsophisticated buyers, but experienced business

people will not put up with this shoddy

treatment in the current buyer's market.

The microcomputer industry is still structured

around the pioneer companies started by a

technically oriented entrepreneur with little cash

and no business experience who ran the business

out of a spare bedroom. These undercapitalized,

understaffed enterprises made millions because

there was no competition, and because the

owners were too busy taking money to the bank

to worry about the customer. Their problem was

how to expand fast enough to meet the unfilled

demands. It didn't matter if the customer was

unsatisfied because the product was already paid

for (they don't give refunds if the product doesn't

work), and there were dozens of new buyers to

replace every lost customer.

Good documentation and customer support are

extremely important for business equipment and

software. With the large number of vendors

competing for your dollar today, your decision to

buy any micro product should be largely based

on how you will be treated by the company after

the purchase. In order to help you compare

customer support policies,

The Computer

Journal

is surveying vendors and will publish the

customer relations policy with the addresses and

phone numbers. We will also encourage them

submit bug fixes, customization notes, and

interfacing information for publication.

Realizing that what happens in the real world

is often different than the published policy, we

will also publish the experiences of our readers,

after giving the vendors the opportunity to

respond. We do need your experiences with

vendors (both the good and the bad) to help

others avoid the companies with poor products

and miserable customer relations.

Our loyalty is to our readers, and not to any

possible advertisers. We will not hesitate to

report bad products and poor customer support,

but we will need copies of correspondence and

records of phone calls which we can present to

the vendors prior to publication.

We have had a bad experience with a

computer system we purchased recently. We

wrote twice for information on an upgrade, but

they have not answered our letters. We liked

their product, but will not purchase any other

equipment from them or recommend their

equipment to anyone else. Weare sending copies

of the letters to the vendor for their reply before

publishing the details.

This magazine is published for you, and it will

only be as good as you make it. Take time to tell

us about your vendor experiences, and share

your

bug

fixes,

customization

patches,

interfacing information and technical tips with

the other readers.

•

EditorlPubluher

A rt Director

Techllical Editor

Productioll Auutallt.

COlltributillg Editor

Art Car180ll

Joall Thomp,oll

Lame Rose

Judie Overbeek

Ernie Brooller

The Computer Jou1"fl4lS

publuhed

times

a year. Anllual ,ub,criptioll

S24

in tile U.S.,

SjO

in Canada, and

S48

airmail ill other

countries.

Entire c01ltent, copyright

1984

by Tile

Computer

JouT7l4l.

Po,tmalter: Send addreu cMnges to: Tile

Computer Joumal. P.O. Box

1697,

Kali8pelJ. MT

5990j-1697.

Addre"

all

editorial, advertiling and

,vb,criptwr. inqvire, to: Tile Computer Joumal.

P.O. Box

1697,

KalilpelJ. MT

59903-1697.

BUILD A VIC·20 EPROM PROGRAMMER

Neil Bungard

...

'III

• .11

Introduction

About a month ago I was presented with an interesting

problem. I had acquired a Z-80 based S-100 bus

microcomputer which had no operating software installed on

it. I had an operating system stored on paper tape, but I

needed the operating system on an EPROM before my

system would run it. The EPROM programmers that I

looked at were too expensive to justify buying simply to

program one EPROM, so I looked for an alternative

solution. It so happened that I had recently purchased a

VIC-20. so I decided to design an EPROM programmer

attachment for the VIC-20 and use the VIC-20 to transfer

the Z-80 operating software from the paper tape to the

EPROM. The VIC-20 solved my EPROM programming

problem with exceptional grace. With the VIC-20 and ten

dollars worth of additional hardware. I was able to enter.

inspect. program. and verify data on both 2716 (2K by 8) and

2732 (4K by 8) EPROMs. In addition. the VIC-20 EPROM

programmer has features not found on even the most

expensive EPROM programmers. Data to be programmed

into the EPROM can be entered from cassette tape.

diskettes. any RS-232 device, from the VIC-20 keyboard. or

even from another EPROM.

Circuit Description

The VIC-20 EPROM programmer circuit diagram is shown

in Figure

This circuit was designed to program 2716 (2K

by 8) EPROMs, but with minor circuit modifications the

VIC-20 can program 2732 (4K by 8) EPROMs as well. These

modifications will be explained in detail. and can be hard

wired or wired so that "personality modules" can be

inserted to select between programming 2716s or 2732s.

The VIC-20 EPROM Programmer performs four basic

functions:

1. It can set the address of where data trasfers are to begin

on the EPROM.

can read data from a "read only" EPROM. This is used

in the EPROM duplicate mode.

can read data from a "programable .. EPROM. This is

used in the program verification mode.

can program an EPROM. This, of course. is used in the

program mode.

To obtain an understanding of the operation of the EPROM

programmer circuit in each mode, let us look at these four

basic functions separately.

The first function. address selection, is accomplished by

loading three presettable counters with the beginning

address of where you wish to store or retrieve data on the

EPROM. The counters are 74LS193s (lC 1.2. and 3 in Figure

1). The inputs of the counters are tied through buffers to the

data bus of the VIC-20. The outputs of the counters are

connected to the address lines of the 2716s so that the

values loaded into the 74LS193s will be present on the

address lines of the EPROMs. With an address value loaded

into the 74LS193s and present on both EPROMs. a memory

read from either EPROM or a memory write to the

programable EPROM can be accomplished. Once the data

transfer operation is accomplished, the selected address can

either be advanced in increments of one. or a new address

can be loaded into the counters.

Values are loaded into selected counters by the VIC-20 via

an Input/Output (I/O) device code generator (IC4). The

device code generator (a 74LS138) is a three line to eight

line decoder. Its three input lines are tied through buffers to

the thrt"e lowest order address bits of the VIC-20 address

bus. When the VIC-20 wants to accomplish an information

transfer leither Input or Output) it places the address of

where the data exchange is to take place onto pins 1. 2, and

3 of the 74LS138. The VIC-20 then pulses "BLK1" to a logic

O. This generates a device code pulse on one of eight output

pins on the 74LS138 which accomplishes a data transfer

to/from one of eight unique address locations defined by the

values of AO. AI. and A2. Table 1 shows the eight data

transfer pulses generated on the EPROM programmer.

Figure 2 is the timing diagram of the device code pulse

generated.

With reference to Table 1. the following software is

required to operate the device select hardware and set a

given address location for a memory transfer:

10 POKE 8195,0

20 POKE 8192.0

This program addresses memory location 0 (decimall on the

EPROMs. 10 POKE 8195,0 loads the four higher order bits

of the 12 bit address into address counter IC3 by placing the

high order address value on data bus bits DO through D3

and pulsing pin 11 of IC3 to a logic O. 20 POKE 8192,0 loads

the eight low order address bits into counters ICI and IC2

OIvlCl

'II

,II

.11

,;J

'''I

Output

Cod.

DIYIc.

Cod.

Pul••

••

Addr•••

14LS13.

15 loads the 8 lower order bits of the address counter

8192

NA NA

8193

13 transfers data from" programmable" EPROM to the VIC 20

8194

12 Loads the 4 higher order bits of the address counters

8195

11 transfers data from" read only" EPROM to the VIC 20

8196

10 programs EPROM and increments the address counters

8197

NA NA

8198

NA NA

8199

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Figure 1

advanced. Details of this sequence will

discussed further

in the explanation of the programming mode.

The important thing to remember in our discussion thus

far is that for the purpose of reading either EPROM, the

READIPROGRAM switch must be in the READ position.

The second instruction 20 FOR I - 0 TO 50: NEXT I

software time delay

allow the monostable

time out

before any other instructions are executed. Even though the

50ms pulse

only used in the programming mode it

still

generated in the read and verify modes

advance the

counters. It is the trailing edge of this pulse that always

advances the address counters and thus must

accounted

for in all the modes of operation.

The second basic function performed by the EPROM

programmer

reading data from the "read only" EPROM.

In order to do this. the memory address of where the read

operation

oceur

loaded into the memory address

c:ounters

previously explained. Next. a memory read

operation

performed by the VIC·20 which generates an

input device code pulse on pin 11 of the device code pulse

generator IC4. Pin 11 of IC4 is connected

the chip select

by placing the EPROM address value on the data bus and

pulsing pin 11 of IC1 and IC2 to a logic

To advance the

counters. which increments the selected address. the

following instructions are required:

10 POKE 8197.0

20 FOR 1-0 TO 50: NEXT I

POKE 8197,0 generates a device code pulse on pin 10 of the

74LSl38 (IC4). This low going pulse triggers a monostable

multivibrator (IC10). which is configured to generate a 50ms

high-going pulse. This 50ms pulse

required in the EPROM

programming sequence which will be discussed later. The

output of the monostable (pin 3, IC10) is connected. through

an inverter. to the "uJrCount" input of ICI.

the

READIPROGRAM switch (Sl, Figure 1)

in the READ

position (open), the selected address will be advanced by one

when the monostable times out. but no EPROM memory

location will be programmed. However. if the

READIPROGRAM switch

in the PROGRAM (closed)

position when the POKE 8197,0 instruction

executed.

address location 0 (decimal) on the programmable EPROM

will

be loaded with a 0 before the address counter (ICI) is

The Computer Journal

BlU

DIu

T,."......

'dati

transl.

AOcIrtIS

=:x

HHoh Z

VIIiOlClGrlU

x:=

programming sequenee is shown in Figure

The

data

applied to the EPROM by the VIC·20 through a memory

write operation to location 8197 (decimal). This memory

write operation generates a device code pulse on pin 10 of

IC4 which latches the outputted data byte into IC7 and

triggers the monostable multivibrator (ICI0l. The

monostable applies a 50ms high·going pulse to pin 18 of the

EPROM and programs the applied memory address with the

data byte latched in IC7. The falling edge of the 50ms

programming pulse automatically advances the counters and

prepares the next memory address for programming. The

following software is required to program address location 0

with decimal value of 100:

10 POKE 8195,0

20 POKE 8192,0

30 POKE 8197.100

0utP\Il

DIu

¥ItIClOl'lI

Oo¥tco

COllI

AdcI_

===x

--w--

F!gUr12: Device Code Pulse Timing.

Figure 3:

2716

Read Timing.

,,,,

(CS) input of the read only 2716 UC6). When the CS input

(pin 20) is pulsed low (with pin 18 tied low and pin 21 held

high) data llows from the memory location addressed on the

EPROM into the VIC·20. Figure 3 shows the timing diagram

of the 2716 read operation. The following software is

required to perform the read only EPROM read operation:

10 POKE 8195,0

20 POKE 8192.0

30 A • PEEK(8196)

The BASIC instructions in lines 10 and 20 set the memory

address of where the read operation will occur. These two

instructions have been previously explained. The instruction

30 A. PEEK(8196) generates a device code pulse on pin 11

of IC4 which inputs the data from the addressed memory

location. and assigns the data to the variable name

"A".

The third basic function performed by the EPROM

programmer, reading data from the programmable EPROM,

is accomplished in exactly the same manner as reading from

the read only EPROM. The only difference is that a device

code pulse is generated on pin 13 of IC4 instead of pin 11 as

in the case of the read only EPROM. Pin 13 of IC4 is

connected to the CS input of the programmable EPROM (pin

20. IC5) and to the output enable (OE) of an octal tristate

buffer (pin 1. IC8). Data flows out of this EPROM and

through the buffer when pin 13 of the 74LSI38 is pulsed low.

For the read operation to be accomplished. pin 18 of the

2716 must be at a logic 0 and pin 21 at

5 volts. The

software required to read data from the programmable

EPROM is:

10 POKE 8195.0

20 POKE 8192.0

30 A • PEEK(8194)

The fourth and last funetion performed by the EPROM

programmer

programming an EPROM. To enter the

program mode. the READIPROGRAM switch must be

placed in the PROGRAM position. This applies

25 volts to

pin 21 of the EPROM UC5). and configures the EPROM

be programmed. Be sure that the 25 volt supply

stable

and at no time fluetuates higher than 26 volts. A volu.e

p-eater

tlwl

Z6 volt.

pia

21 of the EPROM

w01

iauDecUately de.troy the EPROM. Next. as was the case

when reading the EPROMs. the memory address of wbere

the data transfer is

take place must be loaded into the

address counters. By applying an address

the EPROM.

placing pin 21 at

25 volts. and insuring that tbe CS input

at a logic 1. the EPROM is ready

be programmed.

Applying a data byte on DO through D7 of the EPROM. and

pulsing pin 18 (PDIPGM)

a logic 1 for 50ms completes the

programming operation. The timing diagram for the 2716

AppUeatioD Software for the VIC·20 EPROM

Programmer

,<iI

The software required to read. verify, and program 2716

j,,..

EPROMs will be presented in the following discussion on

application software. To perform an EPROM duplication. the

contents of a previously programmed EPROM is transferred

into the VIC·20's RAM memory. Here the data can be''''

inspected and/or modified .if desired. The data is then

j,4

transferred to a blank EPROM. and a verification

accomplished

ensure that no error occured in the data ' 4!

transfer. The following software reads the 2048 memory

locations of a 2716 and places the data into the VIC·20's ."

RAM memory between locations 5000 (decimal) and

7048(decimal). Insure that the READIPROGRAM switch

''4!

in the READ position. and that the EPROM to be read is

,oil

inserted into the read only EPROM socket:

10 PRINT ''''

20 PRINT "SET SWITCH TO"

30 PRINT "READ POSITION"

40 PRINT

50 PRINT "HIT RETURN"

60 PRINT "TO START"

70 INPUT X

80 POKE 8195.0

90 POKE 8192.0

100 FOR 1- 5000 to 7048

110 A- PEEK(8196)

120 POKE I,A

130 POKE 8197.0

140 FOR T- 0 to 50:NEXT T

150 NEXT I

160 PRINT"READ COMPLETE"

170 STOP

clear screen

r·iiI

lensure that

IREAD/PROGRAM

Iswitch is

correct position

lload

high-order 74LS193

lload

low-order 74LS193

set

2048 RAM spaces

Iread EPROM

store value in RAM

ladvance counters

Iwait for 50ms pulse

Ito

read

location

prompt user

,,.

,oil

-00

not enter comments in right hand column as part of

"ill

program.

Once the data is in RAM memory. the user can check the

code

ensure tbat the correct. 2716

being duplicated. ,"

and/or make minor modifications

the code. Once satisfied

with the data in RAM. the data

transferred to a blank ."

EPROM which has been inserted into tbe programmable ,..

EPROM socket. Before the transfer takes place. the

READIPROGRAM

switch must be placed in the

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