Document ID: TOS-LOG-REF-005 Revision: 1.0 Author: ThisOldScot
Section_1: Overview#
Bus Sniffing is the process of monitoring a console’s data bus in real-time to analyse software execution or extract ROM data. However, the Address and Data buses are delicate; attaching a Logic Analyser or a secondary CPU directly to these lines increases the “Electrical Load,” which can distort signals and cause the console to crash.
Buffer Isolation uses high-impedance logic chips (Buffers) to act as a one-way “glass wall.” The sniffer can see the data, but the console’s electrical environment is never touched.
Section_2: Essential Isolation Hardware#
In the Borders Lab, we utilise the 74LVC and 74ALVC families for their high-speed, low-power characteristics.
| IC Model | Type | Function |
| 74LVC244 | Octal Buffer | Provides 8 channels of unidirectional isolation. |
| 74LVC245 | Transceiver | Allows for bi-directional sniffing (Control lines). |
| SN74AXC8T245 | Dual-Supply | Ideal for sniffing 5V buses with 1.8V or 3.3V analyzers. |
Section_3: The Isolation Protocol#
STAGE_3: 01 // The “Observer” Principle#
The buffer must be powered by its own clean power rail, separate from the console’s logic 5V if possible, to prevent ground noise injection.
STAGE_3: 02 // High-Impedance (Hi-Z) State#
Ensure the Buffer’s OE (Output Enable) pin is tied to the sniffer’s control logic. When the sniffer is off, the buffer pins should go to a “Hi-Z” state, effectively becoming invisible to the console.
STAGE_3: 03 // Termination Resistors#
When sniffing long buses (e.g., via the PS1 Parallel Port), place 100-ohm series resistors between the console pins and the buffer inputs.
- The Logic: This prevents “Signal Reflections” from travelling back into the console’s CPU and corrupting the real game data.
Section_4: Forensic Bus Troubleshooting#
If the console works fine until the sniffer is attached:
- Current Draw: Check if the buffer ICs are drawing too much from the console’s 5V rail.
- Capacitance: The input capacitance of the buffer ($C_{in}$) might be too high. Switch to an ALVC (Advanced Low-Voltage CMOS) variant, which typically has lower gate capacitance.
Section_5: Technical Warning#
Safety_Warning
GROUND BOUNCE ALERT: When switching 16 or 32 bits simultaneously at high speed, the sudden current rush can cause “Ground Bounce”—where the ground plane momentarily rises above 0V. This creates false logic triggers. Always place a 0.1uF Ceramic Decoupling Capacitor directly across the VCC and GND pins of every buffer IC.
Section_6: Practical Application: Real-Time RAM Hacking#
To view a console’s internal memory state without pausing the game:
- Bridge the System RAM address and data pins to a bank of 74LVC244 buffers.
- Connect the outputs to a High-Speed Logic Analyzer (TOS-DIAG-003).
- The Result: You can watch the “Enemy HP” or “Player Coordinate” variables change in the sniffer software in real-time, providing deep forensic insight for mod development or exploit research.