TI-Graph Link adapters

This repository contains information about three types of TI-Graph Link adapters:

• TI-Graph Link serial (gray)
• TI-Graph Link serial (black)
• TI USB Graph Link (silver)

Building Firmware

The included makefile build system can build both the Silver Link "B" and the serial Gray Link firmware. The resulting .eep file should be bit-compatible with the EEPROM contents.

Silver Link build dependencies are:

• sdcc: versions 3.8.0 through 4.2.0 have been tested
• GNU make
• Python 3: for the script which generates the Autoexec header and checksum

Gray Link build dependencies are:

• gputils: version 1.5.2 has been tested
• GNU make

$ make
sdas8051 -lops ti_graph_link_silver.asm
sdcc -mmcs51 --code-size 0x1400 ti_graph_link_silver.rel -o ti_graph_link_silver.hex
makebin -p ti_graph_link_silver.hex ti_graph_link_silver.bin
./tools/generate_eeprom.py ti_graph_link_silver.bin ti_graph_link_silver.eep
gpasm  -o ti_graph_link_serial_gray.hex ti_graph_link_serial_gray.asm
ti_graph_link_silver.bin: OK
ti_graph_link_serial_gray.hex: OK

TI-Graph Link serial (gray)

The gray TI-Graph Link cable uses a DB-25 serial connector and works with Windows and Macintosh computers. It includes adapters to connect to DB-9 RS232 serial port on a PC and a DIN adapter to connect to RS-422 serial port on a Mac. Merthsoft's Link Cables page contains additional information about this cable.

Gray Link: Schematic

Full schematic is included in the repository as TI-Graph Link serial (gray) PDF or KiCad.

The control of the cable is provided with a PIC16C54 which receives requests on serial TX, sends responses back on serial RX, and manages the graph link communication on the tip/ring of the 2.5mm cable through two pairs of pins. There are three power supplies on board: 5V regulator for the PIC and graph-link communication and positive and negative voltages for the RS232 communication with the host.

Gray Link: GPIO connectivity

Graph Link	Direction	GPIO	IC Pin
Tip (red)	In	RA0	17
Tip (red)	Out	RA1	18
Ring (white)	In	RA2	1
Ring (white)	Out	RA3	2

Notable parts:

• U1: PIC16C54
• VR1: 5V regulator, likely similar to TelCom TC55
• CR3/CR4: M1M diodes to supply power from RTS/DSR/DTR control lines
• U2, U3, U4, U5, U6: variants of Schmitt trigger inverter

TI-Graph Link serial (black)

The black serial Graph Link cable was the later revision with a female DB-9 connector and is only intended to work with Windows PCs.

Black Link: Schematic

Full schematic is included in the repository as TI-Graph Link serial (black) PDF or KiCad.

• CNTR: connector for serial port control lines
• CR3/CR4: M1M diodes to supply power from RTS/DTR control lines
• C1/C2: bypass caps
• U1: LM339AM single supply quad comparator
• CR6/CR7/CR8: diodes for inverting input and pullups
• R6/R10: pullups for inverting input and link port
• R1/R2/R3/R4/R5/R7/R8/R9: graph link circuitry around LM339
• JACK: 2.5mm 3-conductor graph link jack

TI USB Graph Link (Silver)

There are two hardware models of the Silver Graph Link USB cable: "A" and "B" as denoted by the last character of its production code. Most graph link cables contain a production code on the back label in the following format: FMMYYH:

• F - Factory: I (Taiwan), S (China), P (China)
• MM - Month of manufacture
• YY - Year of manufacture
• H - Hardware: either "A" or "B" (see description below)

The "A" version uses a Cypress CY7C64013 chipset and was manufactured from sometime in the early 2000s through March 2003. Starting around April 2003 through 2010, the "B" hardware version using the TI TUSB3410 was manufactured.

Silver Link "A": Cypress CY7C64013

Some info about the "A" TI Silver Link is documented here: http://merthsoft.com/linkguide/usbdevices/SilverLink%20USB.txt

Silver Link "A": Schematic

Full schematic is included in the repository as "A" Rev 1 PDF or KiCad.

• D1: D3G Rohm Schottky barrier diode RB471E (PDF)
• L4, L4: 2R7 2.7µH inductor
• U1: DQF Voltage Regulator, 3.3V S-812XXSG (PDF) (81233SGUP)
• U2: H8 Rohm Bias resistor transistor IMH8A (PDF)
• U3: CY7C64013 Cypress USB CY7C64013,113 (PDF)
• X1: 6.0F2D 6MHz Crystal

Cypress CY7C64013

Cypress M8 Series (M8 Core w/ 8K EPROM)

The CY7C64013 is a Full-Speed USB microcontroller made by Cypress. It uses a 6MHz external clock source. The CPU uses a proprietary 8-bit RISC M8 architecture and is clocked at 12MHz.

• Cypress Website on CY7C64013
• Cypress Website about USB Programming Tools

GPIO connectivity

Graph Link	GPIO	SOIC Pin
Tip (red)	P0[0]	17
Ring (white)	P0[1]	13

Silver Link "B": TI TUSB3410

Silver Link "B": Schematic

Full schematic is included in the repository as "B" Rev 3 PDF or KiCad.

• D1: D3G Rohm dual Schottky barrier diode RB471E (PDF)
• D2: 3F Chenmko Schottky barrier diode CH461FGP (PDF)
• L1, L2: 2R7 2.7µH inductor
• U1: 24LC64 64kbit EEPROM: Microchip 24LC64 (PDF)
• U2: AQI TI LDO Regulator, 3.3V TPS715 (PDF) (TPS71533DCKR)
• U3: TUSB3410 USB TI TUSB3410 (PDF)
• U4: H8 Rohm Bias resistor transistor IMH8A (PDF)
• Y1: 12.0F4K 12MHz Crystal

GPIO connectivity

Graph Link	GPIO	VQFN Pin
Tip (red)	P3.3	30
Ring (white)	P3.4	29

EEPROM data

The EEPROM data contains a header which is first read by the bootloader in the TUSB3410 ROM. If the header matches the expected format, the size as is described in the header is read out from the EEPROM into Code RAM. The bootloader then jumps to this code.

Autoexec Binary Firmware:

OFFSET	TYPE	SIZE	VALUE	DESCRIPTION
0x0000	Signature0	1	0x10	FUNCTION_PID_L
0x0001	Signature1	1	0x34	FUNCTION_PID_H
0x0002	Data Type	1	0x07	Autoexec binary firmware
0x0003	Data Size(low byte)	1	0x00	0x1400 bytes of application code
0x0004	Data Size(high byte)	1	0x14
0x0005	Check Sum	1	0x5a	Checksum of the following firmware
0x0006	Program	0x1400		Binary application code
0x1406	Data Type	1	0x00	End of header

Silver Link "B": Firmware

TUSB3410 contains an 8052 microprocessor. The application code contained within the EEPROM is responsible for receiving commands over USB and communicating with the calculator over its PORT3 GPIO.

TI USB Graph Link Breadboard Edition

User "okrayo" on the Cemetech forums recreated the TI USB Graph Link "B" on a breadboard using a TUSB3410 and through-hole alternatives for the power supply, transistors, diodes, and passive components. Since this uses the same USB chipset and firmware as the official Silver USB Graph-Link, this works with existing SW and TI graphing calculators with 2.5mm data port.

Component Replacements

The table below enumerates the part replacements that "okrayo" used in the design relative to the original "B" schematic. In addition to these parts, the following modifications were made:

• Added 0.1µF decoupling capacitor between 1V8 and GND
• Removed the L2/C9 L1/C10 filter on tip and ring connections
• Added LED + 330Ω resistor on 3V3
• Left 24LC256 WP pin disconnected to prevent inadvertent writes

RefDes	Description	"B" Part	Breadboard Part
C1/C5	Xtal caps	33pF SMT	22pF through-hole
D2	Suspend Diode	CH461FGP	1N4148
R8/R9	USB D+/D- Res.	22Ω	27Ω
R20/R21	1V8 voltage divider	90.5k/100kΩ	15k/18kΩ
R24	VREGEN Resistor	32.4kΩ	33kΩ
U2	3.3V volt. regulator	TPS71533	MCP17003302E
U4	Transistors	IMH8A	2x PN2222A
U1	EEPROM	24LC64	24LC256
D1	Schottky Diodes	RB471E	2x MBR150

TI USB Graph Link Breadboard Edition: Schematic

Full schematic is included in the repository as TI Graph-Link "okrayo" Breadboard PDF or KiCad.