Texas Instruments TI-83-Plus - Page 105

Chapter 2: TI-83 Plus Specific Information 95
TI-83 Plus Developer Guide Third Release May 28, 2002
• Send and receive bytes of data directly through the port.
This operation involves the application interpreting the data sent and received in a
custom format. This type of communication is for applications that either interacts
with another TI-83 Plus or computer without using the built-in messaging protocol,
which is not documented in this developer’s guide.
The TI-83 Plus link port uses two data lines, D0 and D1, for communicating. These
data lines are accessed through the B-port of the Z80.
– Bits 0 and 1 are for writing/reading data, D0 = bit 0, D1 = bit 1.
For example, the following code shows all of the values that can be written to the
B-port.
LD A,D0LD1L
OUT (bport),A ; is used for setting d0 low, d1 low
LD A,D0LD1H
OUT (bport),A ; is used for setting d0 low, d1 high
LD A,D0HD1L
OUT (bport),A ; is used for setting d0 high, d1 low
LD A,D0HD1H
OUT (bport),A ; is used for setting d0 high, d1 high
Note: Data lines are high when not in use.
For example, the code below will poll the B-port until it detects some activity and
then examine which line has the activity.
IN A,(bport) ; poll the b-port
CP D0D1_bits ; any data line go low ?
JR Z,no_activity ; jump if no activity detected
;
CP D0HD1L ; is d0 high ?
JR Z,d0_low ; yes,
;
; else d1 is high
;