Bus Blaster v1 design
From DP
Bus Blaster v1 is an experimental high-speed JTAG debugger design, it is no longer available. Please see Bus Blaster v2.
- Fully buffered interface works with 3.3volt to 1.2volt targets
- Based on FT2232H with high-speed USB 2.0
- Compatible with 'jtagkey' programmer type in OpenOCD, urJTAG, and more
- Open source (CC-BY-SA)
Bus Blaster v1 is now available to early adopters at a discount. Each unit is tested with a real JTAG target before it ships.
Read about the design below.
Contents |
Overview
| Project Summary | |
|---|---|
| Name: | Bus Blaster v1 design |
| Buy it: | Get one for $35, including worldwide shipping at Seeed Studio |
| Price: | $35, including worldwide shipping |
| Status: | Test production |
| Manufacturing: | Discontinued |
| Forum: | Bus Blaster v1 design Forum |
The Bus Blaster is used to program and debug devices with a JTAG interface like ARM processors, CPLDs, flash memory, and more. It has a JTAGkey-compatible buffer interface that is supported by most popular open source JTAG utilities.
This project was developed in a public forum, and progress was documented on a wiki.
Hardware
Click for a full size schematic image. Schematic and PCB were designed with the freeware version of Cadsoft Eagle, download the latest project files from our Google Code project page.
FT2232H
The FT2232H is a powerful USB to serial communication chip. It has an MPSSE feature that provides a simple USB to JTAG converter (and UART, I2C, or SPI). Most DIY JTAG debuggers use this chip, as do many commercial models.
Bus Blaster v1 uses the 'H' version of the chip, the latest 3.3volt revision that supports JTAG adaptive clocking. The circuit is based on a reference design from the FT2232H datasheet.
We chose not to populate the optional EEPROM on Bus Blaster v1 in order to stay within our price goals. It is not required, and without it the FT2232 uses default settings.
- See the FT2232H breakout board documentation for a complete explanation of the FT2232H reference circuit
Buffered interface
The buffer translates voltage levels between the FT2232H (3.3volts) and a JTAG device (1.2volts-3.3volts). The buffer is the primary difference between the Bus Blaster and a plain FT2232H development board.
The buffer is powered by the target, 1.2volts to 3.3volts only You must connect the target power supply to the JTAG VTG pin
The four main JTAG IO pins (TDI, TDO, TCK, TMS) are at fixed locations on the FT2232, but the other control pins vary among programmers. We wanted the Bus Blaster to work 'out of the box', so we used a buffer compatible with the Amontec JTAGkey style interface.
The jtagkey interface is common among DIY programmers, and it's already supported in most open source JTAG utilities. We reverse engineered the connections from the OpenOCD source code and verified them against the Openmoko debug board v3 schematics.
The buffer is NOT 5volt compatible.
Outputs
| pin | FT2232 pin | description | notes |
|---|---|---|---|
| TDI | ADBUS1 | JTAG data in to target | |
| TCK | ADBUS0 | JTAG clock in to target | |
| TMS | ADBUS3 | JTAG state machine update | |
| TRST | ACBUS0 | Reset output | |
| TSRST | ACBUS1 | Bi-directional reset pin | |
| DGBRQ | ACBUS4 | Debug request | Reserved for future use |
A SN74AVC4T245 level shifter (IC4, IC5) converts 3.3volt FT2232 input to 1.2volt-3.3volt output for the target circuit.
Inputs
| pin | FT2232 pin | description | notes |
|---|---|---|---|
| TDO | ADBUS2 | JTAG data out from target | |
| TSRST | ADBUS6 | Bi-directional reset pin | Connected to TSRST output |
| RTCK | ADBUS7 | System return clock | For adaptive clocking |
| DGBACK | ACBUS5 | Debug acknowledge | Reserved for future use |
| VTG | ADBUS5 | Voltage target detect | Simple transistor with pullup resistor, inverts signal |
Signals from the target to the FT2232 are level shifted by a 74AVC2T45 voltage translator (IC6, IC7, IC8). It is hard-wired to input from the target.
PCB
We used the freeware version of Cadsoft Eagle to make the schematic and PCB. Download the latest designs and firmware from the project Google Code page.
Partslist
Click for a full size placement image.
| Parts | Quantity | Value | Package |
|---|---|---|---|
| C1-C7, C13-C21, C25 | 17 | 100nF | C805 |
| C8 | 1 | 3.3uF | SMC_A |
| C9, C10 | 2 | 27pF | C805 |
| C11, C12, C22 | 3 | 4.7uF | SMC_A |
| IC1 | 1 | FT2232H | LQFP64 |
| IC3 | 1 | LD1117-3.3 | SOT223 |
| IC4, IC5 | 2 | SN74AVC4T245 | TSSOP16 |
| IC6, IC7, IC8 | 3 | SN74LVC2T45DCTR | DCT_R_PDSO_G8 |
| JTAG | 1 | 02x10 shrouded header, male 0.1” | PAK100/2500-20 |
| L1, L2 | 2 | 800mA+ ferrite bead | FB805 |
| LED1, LED2 | 2 | LED | CHIPLED_0805 |
| R1 | 1 | 12K | R805 |
| R2, R9 | 2 | 1K | R805 |
| R3, R4, R5, R7 | 4 | 10K | R805 |
| R6 | 1 | 2.2K | R805 |
| R8 | 1 | 100k | R805 |
| R10, R11 | 2 | 470R | R805 |
| T1 | 1 | NPN transistor, 100mA+ | SOT23-BEC |
| USB | 1 | USB MINI B SMD | MINI-USBB |
| X1 | 1 | 12MHz crystal, small package | 4X6 |
The latest sources and distributors are in the master partlist. See something missing? Please let us know.
Taking it further
We're already hard at work on Bus Blaster v2. The updated design replaces the discrete buffer chips with a CPLD. V2 will be cheaper and more flexible.
Get one!
Bus Blaster v1 is now available to early adopters at a discount. Each unit is tested with a real JTAG target before it ships.
You can get a Bus Blaster v1 for $35, including worldwide shipping.
Your purchases at Seeed Studio keep the open source project coming, we sincerely appreciate your support!
Links
License
Hardware license: CC-BY-SA