DS2705: SHA-1 Authentication Master

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Figure 2. Typical Application Circuit

BATTERY TOKEN PRESENCE DETECTION

Authentication of a battery or peripheral first depends on the authentication host detecting the presence or insertion

(electrical connection) of the accessory to the host unit. The DS2705 supports insertion detection in four ways, two

use the CHAL pin and two use the MDQ pin:

negative logic level is determined by the CHP bit.

2. CHAL pin edge trigger after power-up period. Positive or negative edge trigger is determined by the CHP

bit.

3. Detection of Asynchronous 1-Wire Presence Pulse by insertion of battery with 1-Wire device (token).

4. Periodic Authentication Attempt issuing a 1-Wire Reset on MDQ to test for presence of a 1-Wire token.

With cases 1 and 2 above, the CHAL pin acts as a detection trigger when pulled to a logic low or logic high. A split

contact on the battery ground or supply terminal can be used to connect the CHAL pin to the positive or negative

battery terminal when the battery is present. In case 1, when the battery is connected prior to powering up the host

system (which occurs often since the battery typically powers the host), presence is detected by sensing the logic

level on CHAL immediately after power-up of the DS2705. A configuration bit, CHP, allows the use of either polarity

of the CHAL pin. Table 1 shows the timing and sequence of events for detecting presence on power-up. In case 2

above, the DS2705 monitors the CHAL pin for a signal transition after the power-up period is complete. The

DS2705 detects an authentication attempt on a positive or a negative edge of CHAL depending on the state of the

CHP bit. Table 2 shows the timing and sequence of detecting presence with an edge on CHAL.