TINY-2/MICRO-2 Technical Ref., 2. Ed 1989
- 22 -
If the packet controller's sign-on message lines appear to be typed over each other, you should set
the packet controller command AUTOLF ON. If the sign-on message appears to be double-spaced,
you should set AUTOLF OFF. If the sign-on message appears to be single-spaced, AUTOLF is cor-
rect.
The Controller won't accept commands
After the packet controller signs on, try giving it any command. If the default settings are in effect,
it will attempt to echo each character you type back to the screen. If it doesn't echo, be sure that
the SIO (U14) pin 23 has a voltage level between 0 and +0.4 Volts on it. The voltage on MAX231
pin 5 should be greater than +3 Volts. If these conditions are not met, check the cable wiring and
refer to the section about terminal interface troubleshooting.
If the above checks are OK, use an oscilloscope to verify that data is present on SIO (U14) pin 28
and MAX231 (U15) pin 10 when you strike a key on the computer. If not, the data isn't getting
from the computer to the packet controller. Check the serial connector in use (P4-RS-232, or P3-
TTL), the cable and MAX231 (U15) again. Finally, be sure that the computer actually uses levels
less than -3 Volts and greater than +3 Volts for signal levels. 0 and +5 Volts will not work unless
the TTL port is used.
Other Symptoms
TINY-2/MICRO-2 appears dead
If no LEDs wink during the start-up cycle the problem is more serious. Check to see that the crys-
tal oscillator is working (4.1952 MHz) and that the signal appears on the output of U7 (74HC4060)
pin 9. The clock signal is a (possibly distorted) square wave signal. Also check for clock signals Z80
CPU (U1) pin 6 and SIO (U14) pin 20.
Verify that the battery backed-up RAM protection circuit is working by measuring that pin 28 of the
RAM (U8) at least +4.7 Volts after input power is applied.
If the unit is operating and accepting commands from the terminal, an overall check of the CPU
complex may be conducted using the HEALTH command (see Operating Manual).
Modem won't kev transmitter
Check to see the commands XMITOK and TXUIFRAM are ON. If the transmitter doesn't key, the
problem is most likely in the connecting cable, or a carrier present (DCD) indication. If DCD is ac-
tive and the command FUlldup is off, the controller will not activate the keying line. If this is the
problem, see the DCD section below. If the connections appear to be in order, check 8440 (U14)
pin 17 for keying (PTT) transitions. If nothing is seen on pin 17, either software or digital hardware
are faulty. If pin 17 is active, trace the signal through 74HC14 (U17) pin 9 to U17 pin 8 (now in-
verted) to the gate of the keying FET (Q2). The FET output line changes from high impedance to
low when a keying signal is present. This can be checked with an Ohmmeter.
Uncopyable transmitted packets
If other stations seem unable to decode your packet transmissions, it is possible that your trans-
mitter is being overdriven. Listen to the sound of your TINY-2/MICRO-2 transmissions on another
receiver. Extremely weak signals indicate inadequate modem output. Refer to the Transmit Level
Adjustment Procedure. You may also be able to hear the beginning of transmissions clipped or
weak if inadequate transmit delay (RXD command) is being used for your transmitter. You can con-
firm that the digital logic and modem on the packet controller are operating properly by perform-