Radio Shack TRS-80 PT-210 Service Manual page 34

Parity Check and Error Indication
This equipment is provided with the parity check function. Parity check has three modes (i.e., EVEN. ODD,
and NONE) and any one of them may be selected by moving a switch to the desired choice.
*
Parity Check
- % - ' \
/ - - + - ' - v - ' -
START
^V
Parity STOP (STOP Bit)
Bit DATA Bit
Bit Bit
Figure 26.
EVEN check: Parity error lamp lights up when DATA Bit -I- Parity Bit
=
Odd number.
ODD check: Parity error lamp lights up when DATA Bit 4- Parity Bit
=
Even number.
NONE:
No parity check is made. (No error indication is made.)
(Caution: Parity error lamp will not go out if the parity check mode is switched to NONE
while it is lit.)
Error Indication
When a parity error occurs, the following situations arise.
1. The error lamp (LED) is kept lit.
2. The printer prints backward question marks.
NOTE: Reset cannot be made unless power is OFF.