Radio Shack TRS-80 Service Manual page 14

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Specific Symptoms and Suggestions
Extra Characters Dis,layed
If pressing one key results in a substitute character or
characters on the screen suspect the Baud Rate. Procede as
follows:
Set the DT-1 for Half Duplex from Set-Up Mode. Then press a
key.
If the key you pressed is displayed along with one or more
stray characters, then the Baud rate is probably wrong.
Wrong cursor Moves, Bad Commands, etc.
Some Host systems will send End-Of-File terminating codes
that are not compatible with the emulation mode you are
using. For example, suppose you are using the Terminal to
read data stored in some Host system. The cursor jumps
suddenly to the top of the screen and begins overwriting
data already present on the screen. The DT-1 has received a
code that homed the cursor.
There are two approaches to this problem.
1. Reconfigure the Host to match the emulation mode you are
using. CompuServe and most other communications services
have a setup program that will modify the Host for your
terminal. Some systems can be instructed to operate in DUMB
mode. In this mode the Host will not transmit any cursor
positioning sequences at all. In CompuServe, this is done
by appending ",TTY" to the user ID.
2. Change emulation modes through the Set-Up Mode to match
the Host system's requirements.
Buzzer ON Continually
This could result from one of the following:
The MPU (U-12) is not working.
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