Assembling the Handy Board, Part 1
Power, Power Monitor, CPU, and Serial Line Circuitry
This is the start of the assembly sequence for the main Handy Board
unit. In this assembly sequence, the 6811 power supply and power
monitoring circuitry, the 6811 itself, and the serial communications
circuitry will be installed.
For this assembly sequence, collect the following parts:
- Resistors--all resistors are 1/8 watt unless noted
R1 (2.2M--red, red, green)
R2 (1K--brown, black, red)
R8 and R15 (47 K--yellow, purple, orange)
R13 (47 ohm--yellow, purple, black)
R14 (47 ohm--yellow, purple, black, 1/2 watt)
RP4 (1 K x 4 resistor pack, 8 pins, labelled ``102'')
C1 and C2 (22 pF, labelled ``220'')
Note: these are only provided if X1 is a
crystal. If X1 is a ceramic resonator, these are not
C3 (470 µF, axial electrolytic)
C7 and C9 (0.1 µF, labelled ``104'')
C8 (4.7 µF, tantalum, labelled ``4µ7'')
- Diodes and LEDs:
D1 (1N914 signal diode, glass casing)
D3 (1N4001 power diode, black casing)
LED10G (HLMP-1790, green)
LED11R (HLMP-1700, red)
LED15Y (HLMP-1719, yellow)
- Integrated Circuits:
U1 (MC68HC11A1FN or MC68HC11E1FN microprocessor)
U12 (DS1233-10 voltage monitor)
U13 (LM7805CTB 5 volt regulator)
- Connectors and Sockets:
J5 (RJ11 telephone jack, top entry)
J12 (coax DC power jack)
PLCC (52-pin plastic leaded chip carrier socket)
SW1 (silver/red SPDT slide switch)
SW3 (pushbutton switch)
X1 (8 MHz crystal or ceramic resonator)
Microprocessor Power Circuitry
The first order of business is to install the microprocessor power
supply and battery charge circuit. The Handy Board battery will not be
connected until the end of the overall assembly job, however; instead,
power will be supplied to the board through the battery charge circuit.
Install C3*, C7,
C8*, C9, LED15Y*,
D3*, R13, J12,
Mount R14, raising it about 1/8'' above
the surface of the board; it will need to be pressed a bit to
the left when J6 is installed later.
Mount U13*, the main power regulator, so that its
tabbed side is closer to SW1, as indicated in the
Apply power to the board from the adapter jack and switch the board on
using SW1. For a brief instant each time the board is
switched on, the CHARGE LED (LED15Y)
should flash. This indicates power flowing into the board, which in this
case is used to charge C3, the main system capacitor.
Turn the board on, and measure the system power voltage. A convenient
place is the terminal marked +5v and GND
on the connector for U4 (the LCD display). The voltage
should read between 4.9v and 5.1v.
If the CHARGE LED does not light, first check the
polarity on the DC adapter. Set the voltmeter to a 20 volt range and
measure the output of the adapter. The center opening should be the
negative terminal and the outer shield should be the positive terminal.
If these are reversed, the adapter cannot be used to supply power to the
Handy Board via its charge jack. The adapter still may be used with the
If the adapter polarity is correct, check that LED15Y
is installed with the correct orientation.
If the system voltage does not read between 4.9v and 5.1v, check the
orientation of U13. Touch the tab of
U13, if it is getting hot, remove power immediately.
Either U13 or D3 is probably installed
Voltage Monitor Chip
U12, the Dallas Semiconductor DS1233-10, is a voltage
monitor chip that measures the system voltage and asserts a reset signal to
the microprocessor whenever the voltage is invalid (i.e., below 4.5v).
This ensures that the microprocessor is idle during power-on, when system
voltage is ramping up from zero volts to its normal operating level, and
during power-off, when system voltage falls from normal operating level to
The output of the voltage monitor chip is connected to an LED
(LED11R, marked BATT). When the chip
asserts the ``invalid'' signal, the BATT LED will light.
This happens for a brief interval when power is switched off, and for 1/3
of a second when it is switched on. The BATT LED also
serves as a low-battery indicator, since if the battery is not charged
enough to raise the system voltage to its normal operating level, the
DS1233 chip will continuously assert the signal that lights the
Unplug the DC adapter, if it is still plugged into the board. Install
U12*, R2, and LED11R*.
Plug the DC adapter back into the board, and switch it on. The
BATT LED should light for about 1/3 of a second, and then
go off. Switch the board off; the BATT LED should light
and then fade as board power dissipates.
If the BATT LED does not light as it should, check its
orientation, as well as the orientation of U12.
Microprocessor and Oscillator Circuit
In this assembly step, the microprocessor and its oscillator circuit
are installed. The testing step assures that the microprocessor is
correctly driving the oscillator circuit, which is the first indication
of its proper operation.
Unplug the board, if it is still plugged in. Install
PLCC*, the square, 52--pin socket for U1
(the 6811 microprocessor). Make absolutely sure to get the
orientation correct: the chamfered corner (i.e., the diagonally
truncated corner) of the socket must align with the
chamfer in the socket outline printed on the board. The chamfered corner
installs in the upper left when viewing the board from the normal reading
orientation indicated by the photographs.
The socket must be installed correctly because the 6811 can only be
placed into the socket in one orientation, so the socket orientation
must be correct.
Solder all 52 pins of the socket.
Install U1, the 6811 microprocessor, into its socket,
aligning the chamfered corner with the one on the socket. Press
firmly and evenly until the 6811 is fully seated in the socket. It
should click into place.
Install R1 (2.2M--red, red, greem).
Install X1, which may be either a ceramic resonator
(rectangular plastic package with three leads) or quartz crystal (oval
metal package with two leads).
In the photograph, X1 is the ceramic resonator.
- If X1 is the crystal,
install X1, C1, and
- If X1 is the ceramic resonator, install
X1 only. C1 and
C2 are not used because they are already built
into the resonator package. Do not install anything in the
C1 and C2 component positions.
Apply power to the board through the charge jack and turn the board on. By
examining the system clock output of the 6811 (known as the E
clock), the following test will verify that the 6811 oscillator
circuit is operating properly. The E clock signal is at pin
5 of the 6811. It should be a 2 MHz square wave.
In order to test this signal, either an oscilloscope, logic probe, or
voltmeter are required, in declining order of preference (i.e., the
oscilloscope is best).
Note that cases (2) and (3) do not measure the actual frequency of the
signal. It will be assumed that if the clock signal is indeed generated,
it is of the proper frequency.
- With an oscilloscope, measure the E clock signal. It should
appear as a 2 MHz square wave over the zero to +5v range.
- With a logic probe, examine the E clock signal. The
pulse output LED of the logic probe should flash, indicating
oscillation. (Make sure that the logic probe's pulse memory
feature is turned off.)
- With a volt meter, put it in a DC voltage range and
measure the E clock signal. It should register as a 2.5v signal.
The behavior of LED15Y (CHARGE) and
LED11R (BATT) should be as before.
If the E clock signal is not present, this could indicate faulty
soldering between the crystal or resonator and the 6811, or an improper
value of the biasing resistor R1.
It is less likely but still possible that the 6811 is defective.
First check that the 6811 is receiving power and ground properly (on pins
26 and 1, respectively). To measure the ground, use the logic probe to
verify a definite logic low, or measure the potential from the +5v supply.
As a last resort, try another 6811.
Serial Line and Stop Switch
In the next step, circuitry is installed that allows the 6811 to
communicate over a serial line to the host computer. This includes a green
LED to indicate when the 6811 is transmitting data, and a pushbutton switch
that allows the 6811 to be placed into a special ``bootstrap'' mode. This
bootstrap mode allows the 6811 to accept an initial operating program that
is downloaded by the host computer.
Remove power from the board. Install R8,
R15, RP4, D1*,
LED10G*, SW3, and J5.
Apply power to the board and turn it on. LED10G, labelled
PWR, should light. Now hold down SW3
(STOP) and turn power on. Continue to hold the
STOP switch while the BATT LED cycles on
and then off. The PWR LED should turn off when the
BATT LED turns off. This indicates that the 6811 has
entered bootstrap mode, and is waiting for a program to be downloaded over
its serial line.
Back at the host computer, connect the Interface/Charger board to a
serial port using the appropriate modem cable. Connect the DC adapter
power to the Interface/Charger board.
Connect the main board to the Interface/Charger board using the
4--wire telephone cable. Power will be supplied to the main board via
the telephone cable. Put the board in download mode by turning it on
while holding down the STOP switch. The Handy
Board's PWR and BATT LEDs should
both light for about 1/3 of a second, and then both LEDs should turn
off. This state, in which board power is on but both LEDs
have turned off, is the mode required for bootstrap download to
Now run the appropriate version of the 6811 downloader software.
During the first download phase, the green SER LED on
the I/C board (transmit from the host computer to the 6811 board) and
the green PWR LED on the main board (transmit from
the 6811 board to the host computer) should both blink visibly.
The downloader software should reach the second download phase
in which it attempts to download the pcode_hb.s19 program.
It will then generate an error, because the Handy Board does not have
memory to receive this program.
But the point of this test is to see if the downloader reaches the
second phase. If it does, congratulations! Serial communication
between the host computer and the 6811 board has been established.
This is a big step in the process of bringing up a new Handy Board.
There are a lot of things to get right in this step. Most likely
problems involve software configuration (i.e., choosing the correct
serial port) and cabling (using the proper modem cable to connect the
Interface/Charger Board to the host computer; having a telephone cable
that is wired correctly).
Fred Martin /
MIT Media Laboratory /
Tue Jul 16 12:26:48 1996