Epson C82305 - Manual (Page 19)

With the status flag set, and data reception prohibited,
the vacant area of the buffer gradually increases as the
printer continues to print. When the vacant area in the
buffer reaches the specified value (typically 512 bytes;
refer to your printer manual), the flag is reset and data
entry is again enabled.
Note
Reverse Channel pin (No. 11) and DTR pin (No. 20) are
internally connected on the interface board and must
have identical signal levels.
Printer status error
The flag will be set immediately regardless of the
remaining buffer capacity if the printer detects an error.
16