TINY-2/MICRO-2 Technical Ref., 2. Ed 1989
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Step 2: Power Supply
The first thing to check in any malfunction is the power supply.
NOTE: A frequent problem is the use of a poorly filtered or undervoltage DC power supply.
Check that the voltage under load is not low and that excessive ripple is not present. Check the
power supply levels at the output of the voltage regulator. Do all the ICs in the suspected area
have the proper voltage on their power pins? Is there excessive ripple in any of the DC voltage
lines? If so, check the regulator and associated components, working backwards toward the input
power switch. If the voltage is low, in conjunction with a hot regulator, suspect a short Circuit on
the board.
Computer Terminal Interface
If you can't get the packet controller to sign on and accept data from the terminal or computer,
the problem may be in the serial interface.
NOTE: The primary cause of non-communication between the packet controller and the computer
is improper cabling setup.
Inspect the interconnection cabling. Does it work on another controller or RS-232 device? Has the
radio and/or computer been successfully used on packet with this or another packet controller?
Are all the connections tight? Has the cable frayed or broken?
Packet Controller won't sign on to the computer
If you find the TINY-a/MICRO-2 won't send data to the computer, but appears to operate property
as described in General Tests above, verify that the CTS line at RS-232 connector P4 pin 8 or TTL
connector P3 pin 4 is not being held low. The packet controller will not send data to the computer
unless its CTS line is asserted. If the computer does not implement the RTS/CTS protocol, the
RTS/CTS lines (pins 7 and 8 on P4) should remain unconnected to the computer or else tied to-
gether.
Check the baud rates set on the packet controller and computer terminal. Some mismatched com-
binations of baud rate on controller and terminal will cause nothing to be displayed.
If the above checks are ok, observe pin 26 of the SIO (U14) with an oscilloscope and cycle the
packet controller power switch. Transitions on this pin shortly after reset indicate that the packet
controller is sending data. If no signal transitions are seen, recheck that the CPU appears to be op-
erating {see below.) If data appears to be present, verify that TTL transitions are also present on
the MAX231 (U15) pin 8 and RS-232 Signal transitions are present on MAX231 (U15) pin 11 and
P2 pin 2.
The Controller prints only gibberish
This indicates that some combination of the data rate (terminal baud rate), parity option, or num-
ber of start and stop bits are not set the same at the packet controller and at the computer termi-
nal. Verify that the computer terminal is set for eight data bits, no parity, and 1 stop bit. These set-
tings may be made with DIP switches, jumper pins, or software commands depending on the com-
puter terminal in use. The above settings are the default sign-on settings stored in the TINY-2/
MICRO-2 EPROM. Perform a hard reset by pressing the power switch OFF then ON (out then in).
The sign-on message should appear.
