1.2.5 SWI-PWM Interface

Communication with Microchip’s ECC204 in SWI-PWM mode is at 125 Kbps.
  • ECC204 7-Bit Address 0x33 (Write 0x66, Read 0x67)
Figure 1-7. SWI-PWM Connection

Parasitic Power

The ECC204 has the capability to use parasitic power on the SWI-PWM device. The Parasitic Power mode removes the need for a dedicated power source to the crypto device. Power is supplied to the device by capacitor C5. The capacitor is charged when SIO_2 (SIO-PWM mode) is higher than VCC_DVC. For proper operation, VCC_DVC must always be greater than the minimum supply operating voltage of the device. See the specific device data sheet for more details and recommendations.

Figure 1-8. Parasitic Power Boost Circuitry

Follow these guidelines for proper circuitry usage:

  1. The device must be in Parasitic Power mode (remove jumper JPP1).
  2. The EPP# signal must be initially asserted HIGH.
  3. Issue a cryptography command.
  4. Assert the EPP# signal LOW for the duration of the command.
  5. Assert the EPP# signal HIGH.
  6. Read back the command response.
Tip: The Parasitic Power Boost circuitry in general will not be needed. It is recommended that the EPP# signal be driven HIGH or allowed to float to disable the parasitic power circuitry if present. Special software will need to be written to incorporate control of the boost circuitry. This circuitry, in general, will be depopulated on the board.