TI-8x Graphing Calculators
The TI-8x series graphing calculators from Texas Instruments are powered by a derivative of Zilog's Z-80 microprocessor (except the TI-89). There exists a cadre of aficionados creating games and programs both in TI basic and Z-80 assembly language. TICALC is a good place to start your snoop.
TI-8x calculators also connect to TI Calculator-Based Laboratory (CBL and CBL2) modules. Data probes from TI and Vernier can be used to measure pH, dissolved oxygen, temperature, etc.
TI makes a Graph-Link cable and software to allow communication between a TI calculator and a PC or Mac.
I've written these programs to provide a more robust CBL connection.
- Capture single readings from the CBL. A text copy of capture.
- Dgraf gathers CBL data approx. every second and allows graphing. A text copy of dgraf.
- Dgraf uses a CBL checking program you will want to download also. A text copy of cblchk.
TI Graph Link Communication Reference Websites
The sites below provide complete and likely accurate background on the TI Graph Link Communication Protocol.
- Paul Singer's Oregon State University site.
- TiLP is an open-source software project for PC to TI communication.
- Some work I have done with the protocol hardware layer.
- Normally both devices (TI-Calc and PC) monitor the signal lines for activity.
- To begin communication, a device brings one of the signal lines low. Either the TI-Calc or the PC can drop a signal line and either signal line can be brought low. The device dropping the first line is the Master and will control further communication.
- The device on the other end (the Slave) drops the line the Master did not control.
- If the Master drops the "1" line the first bit it is sending is a "1"
- If the Master drops the "0" line the first bit it is sending is a "0"
- After changing the state of a signal line, a device waits for the other device to acknowledge on the other signal line. Failure to do so causes a time-out error. The time-out interval is long enough for either device to service interrupts or higher priority tasks. Nice.
- Timing Diagram (eight bit, no parity)