DS1963S

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Overdrive Skip ROM [3Ch]

On a single-drop bus this command can save time by allowing the bus master to access the memory

functions without providing the 64-bit ROM code. Unlike the normal Skip ROM command the Overdrive

Skip ROM sets the DS1963S in the Overdrive Mode (OD = 1). All communication following this

command code has to occur at Overdrive Speed until a reset pulse of minimum 480 µs duration resets all

devices on the bus to regular speed (OD = 0).

When issued on a multidrop bus this command will set all Overdrive-supporting devices into Overdrive

mode. To subsequently address a specific Overdrive-supporting device, a reset pulse at Overdrive speed

has to be issued followed by a Match ROM or Search ROM command sequence. This will speed up the

search process. If more than one Overdrive-supporting slave is present on the bus and the Overdrive Skip

ROM command is followed by a read command, data collision will occur on the bus as multiple slaves

transmit simultaneously (open drain pulldowns will produce a wire-AND result).

Overdrive Match ROM [69h]

The Overdrive Match ROM command, followed by a 64-bit ROM sequence transmitted at Overdrive

Speed, allows the bus master to address a specific DS1963S on a multidrop bus and to simultaneously set

it in Overdrive Mode. Only the DS1963S that exactly matches the 64-bit ROM sequence will respond to

the subsequent memory or SHA function command. Slaves already in Overdrive mode from a previous

Overdrive Skip or a successful Overdrive Match command will remain in Overdrive mode. All Over-

drive-capable slaves will return to regular speed at the next Reset Pulse of minimum 480 µs duration. The

Overdrive Match ROM command can be used with a single or multiple devices on the bus.

Resume Command [A5h]

In a typical application the DS1963S needs to be accessed several times to complete a monetary

transaction. The number of accesses increases further if host/user-Authentication is also performed. In a

multidrop environment this means that the 64-bit ROM sequence of a Match ROM command has to be

repeated for every access. To maximize the data throughput in a multidrop environment the Resume

Command function was implemented. This function checks the status of the RC bit and, if it is set,

directly transfers control to the Memory and SHA functions, similar to a Skip ROM command. The only

way to set the RC bit is through successfully executing the Match ROM, Search ROM or Overdrive

Match ROM command. Once the RC bit is set, the device can repeatedly be accessed through the Resume

Command function. Accessing another device on the bus will clear the RC bit, preventing two or more

devices from simultaneously responding to the Resume Command function.

1-WIRE SIGNALING

The DS1963S requires strict protocols to ensure data integrity. The protocol consists of four types of

signaling on one line: Reset Sequence with Reset Pulse and Presence Pulse, Write 0, Write 1, and Read

Data. Except for the presence pulse the bus master initiates all these signals. The DS1963S can

communicate at two different speeds: standard speed and Overdrive speed. If not explicitly set into the

Overdrive mode, the DS1963S will communicate at standard speed. While in Overdrive Mode the fast

timing applies to all waveforms.

The initialization sequence required to begin any communication with the DS1963S is shown in Figure

11. A Reset Pulse followed by a Presence Pulse indicates the DS1963S is ready to receive data, given the