Radio Shack TRS-80 Model II Reference Manual page 202

Modell! TRSDOS
Entry Conditions
B = Row on screen to start displaying the buffer, B<24. If B>23, then
B modulo 24* is used as row position.
C = Column on screen to start displaying the buffer. In 80 character/
line mode, C < 80. For C) 79, C modulo 80 is used as column
•
position.
In40 character/line mode, C < 40. ForC > 39, C modulo 40 is used
as column position.
D = Length of buffer, in range [0,255]
(HL) = Beginning of text buffer. The buffer should contain codes below
X'SO'
or the special control codes above
X'FR'.
Any value outside
these ranges will cause an error.
A= 10
Exit Conditions
NZ => Error (invalid character sent)
A = Error Code
*
Modulo-
A cyclical counting system. For modulus
n, x
modulo
n
is the
integer remainder after division of x by n. For example, 85 modulo 80=5.
238