Rainbow Electronics DS2705 - Manual (Page 8)

DS2705: SHA-1 Authentication Master
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Table 1. Presence Detection/Authentication on Power-up Using CHAL Pin
TIME FROM
POWER UP
CHAL PIN
CHP
BIT
TOKEN
PRESENCE
AUTHENTICATION DISPLAY
t = N/A High 0 Not Present Armed Hi-Z
t < t
CHD
Low 0 Present Initiated Hi-Z
t
CHD
> t > t
CHD
+ t
AAT
Low 0 Present In Progress Hi-Z
t > t
CHD
+ t
AAT
Low 0 Present Complete Active
t > t
CHD
+ t
AAT
Pos Edge 0 Removal Reset Reset (Hi-Z)
t = N/A Low 1 Not Present Armed Hi-Z
t < t
CHD
High 1 Present Initiated Hi-Z
t
CHD
> t > t
CHD
+ t
AAT
High 1 Present In Progress Hi-Z
t > t
CHD
+ t
AAT
High 1 Present Complete Active
t > t
CHD
+ t
AAT
Neg Edge 1 Removal Reset Reset (Hi-Z)
t
AAT
: Authentication attempt time represents the period for attempting authentication and is dependent on the
RTA1:0 bits. Minimum time is t
SHA
, maximum time is 8*t
SHA
.
Table 2. Insertion Detection/Authentication Using Transition On CHAL Pin
CHAL PIN CHP BIT TOKEN PRESENCE AUTHENTICATION DISPLAY
High 0 Not Present Armed Hi-Z
Neg Edge 0 Insertion Initiated Hi-Z
Low < t
CHD
+ t
AAT
0 Present In Progress Hi-Z
Low > t
CHD
+ t
AAT
0 Present Complete Active
Pos Edge 0 Removal Reset Reset
Low 1 Not Present Armed Hi-Z
Pos Edge 1 Insertion Initiated Hi-Z
High < 0.5s 1 Present In Progress Hi-Z
High > 0.5s 1 Present Complete Active
Neg Edge 1 Removal Reset Reset
Detection cases 3 and 4 occur through a 1-Wire Reset/Presence Detect sequence on the MDQ pin. In case 3, an
asynchronous 1-Wire presence pulse occurs when a battery with a 1-Wire device is connected to the DS2705. The
DS2705 responds with the authentication sequence. Case 4 is a user configuration option where a 1-Wire reset is
periodically issued on MDQ which then monitors the bus for the presence pulse issued by any/all 1-Wire slave
devices on the bus. If the DS2705 detects a presence pulse, it begins an authentication sequence. The DS2705
can also be configured to periodically test for the continued presence of a 1-Wire slave device once successful
authentication has completed. This allows the status display to be automatically reset when a slave token has been
removed. Table 3 shows the sequence and display activity for presence detection on MDQ.
Table 3. Asynchronous And Periodic Presence Detection Using MDQ Pin
PD
TOKEN
PRESENCE
AUTHENTICATION DISPLAY
No PD Not Present Reset Hi-Z
Insertion Initiated Hi-Z
In Progress Hi-Z PD
Present
Complete Active
No PD Removal Reset Reset (Hi-Z)