Elf Turns 30 ------------------------------------------------------------------------------------------------
Installed if you have a CDP1861/STG1861.
Installed (connects INPUT to EF4).
Unused (doesn’t exist on the current PCB).
Installed (automatically start the monitor
after power up).
Unused for CDP1802 CPU.
Connect RxD to EF3.
Same as JP1.
Same as JP1.
for each subsystem.
After you finish
assembly, apply power
before you install any
ICs and use a DC voltmeter to verify that the
voltage between pins
20 (negative) and 40
(positive) on the microprocessor (CDP1802)
socket is between 4. 9
and 5.1 volts. Remove
power and install all
ICs except the CDP1802, CDP1861
(if you have one), and the TIL311
displays. Turn on the power and check
that the current consumption is about
100 mA. If you don’t get these results,
then stop and figure out what’s wrong
before proceeding. Finally, turn off the
power once more and install the
If your Elf 2000 has a switch
panel, then you can do a few simple
tests with the switches to verify that
everything is working correctly. If you
don’t have a switch panel, then just
skip ahead to the paragraph on the
POST in the next section.
Ensure that all switches are set to
the OFF position, including D0-D7,
and turn on the power — only the SC0
LED should be illuminated and the
address display should show 0000 (the
data display may be any random
value). Flip LOAD to the ON position
and the LOAD LED should
light. Press or flip the
INPUT switch and the display should read 0000 00.
Now set all the D0-D7
switches to ON and press
INPUT again; the display
should now read 0001 FF.
Next try $A5 on the data
switches and press INPUT
and the display should
show 0002 A5. Finally, try
$5A and INPUT and
the display should show
Set LOAD to OFF, Memory
Protect to ON, then flip LOAD back to
ON and the display will show 0000
5A. Press INPUT and the display will
show 0000 00 — this is the contents of
RAM location 0. Try pressing INPUT
three more times and you’ll see the
next three bytes that you just entered;
0001 FF, 0002 A5, and 0003 5A.
Congratulations — your Elf 2000 can
store programs in memory!
TABLE 1. Default Jumper Settings.
at construction, you might want to
download the Elf 2000 User’s Manual
com and read the Assembly section. It
contains many tips for the beginner
on parts selection, preparation, soldering, testing, and debugging.
Although the complete Elf 2000
may seem complex, it breaks down
easily into many separate subsystems.
Most of the subsystems in the Elf 2000
— including the video, EPROM, battery
backup, switches, address and data
displays, and RS232 port — are optional and can be omitted to simplify construction. In a few cases, such as the
battery backup, it’s necessary to add a
few jumpers to the Elf 2000 to ensure
that the rest of the circuit still works
when a particular part is omitted. The
Elf 2000 User’s Manual gives the
details on this and also contains a list
of the exact parts that can be omitted
If you’re using the Elf 2000
EPROM, then first ensure that all the
PCB jumpers are set as shown in Table
1. These settings are necessary for the
monitor to work and you can find
more information about them, including photos of the correct settings, in
the Elf 2000 User’s Manual.
Connect an RS232 terminal or
your PC to the Elf 2000 serial port and
set the terminal or terminal emulator
software for 2400 baud, 8-N-1 (eight
data bits, no parity and one stop bit). If
you have a switch panel, set all Elf 2000
switches to OFF except RUN, which
must be ON, and turn on the power.
The RUN LED should light and the data
display should show 99, followed by
98, and steadily count down to 16.
This count is the “Power On Self
Test” executing, and if the count stops
at any point before 16, then you have
a hardware problem. If you need it,
the Elf 2000 User’s Manual contains a
full list of the 30 some POST codes to
help you debug your Elf 2000. POST
code 16 means that the monitor is
ready for auto baud; press the ENTER
(carriage return) key on your PC
or terminal and you should see
something like this:
COSMAC ELF 2000 EPROM V85 CHECKSUM
7D14 SRAM 32K INITIALIZED
Copyright (C) 2004-6 by Spare Time
Gizmos. All rights reserved.
ElfOS BIOS Copyright (C) 2004 by
For help type HELP.
FIGURE 1. A closeup of
the PC board alone.
Congratulations! If your Elf 2000
passes the Power On Self Test, you