Reset

and

Presence

signals

0

0

1

1

0

0

1

1

Skip ROM (CCh)

Figure 6-9. SKIP ROM Sequence

6.5.3.4 SEARCH ROM Command [F0h]

The SEARCH ROM command helps to identify the number of devices and the 64-bit unique ID of each of the

devices during the initial system bring-up when the host is not aware of the number of devices on the SDQ

bus. The SEARCH ROM command sequence begins with the host generating the RESET pulse of at least 480

μs. All the responder devices on the SDQ bus responds with a PRESENCE pulse. Next, the host continues by

issuing the SEARCH ROM command, F0h. Following the SEARCH ROM command, the host issues three time

slots for each bit of the 64-bit serial ID as shown in Figure 6-10. In the first time slot, the responder devices

begin transmitting the bit of the 64 serial ID starting with the least significant bit. In the second time slot, the

responder devices transmit the complement of the bit. In the third time slot, the host writes the bit to be selected.

The process continues until the end of the 64-bit serial ID. All the responder devices that do not match the bit

written by the host in the third time slot exits from the search process. If the host read zeros in the first two

time slots, then a collision condition has occurred. The host knows there is more than one device on the SDQ

bus. By choosing the bit value to write, the host is branching out to eliminate one or more contending responder

devices. At the end of the first run sequence, the host knows the serial ID of a single device. The sequence is

then repeated to identify the serial IDs of the remaining devices on the SDQ bus.

BIT0

Reset

and

Presence

Signals

0

0

0

0

1

1

1

1

BITn

BIT63

Search ROM (F0h)

Data Read

Figure 6-10. SEARCH ROM Sequence

6.5.3.5 RESUME Command [A5h]

When there are multiple responder devices on the SDQ bus, the RESUME command, A5h, can be used to

maximize the data throughput by reducing the number of bit transactions needed to select the responder device.

Before issuing the RESUME command, the host must first select the responder device by issuing the MATCH

ROM or OVERDRIVE MATCH ROM command sequence. This selects the responder device. All other responder

devices do not respond to subsequent memory function commands and RESUME command function.

6.5.3.6 OVERDRIVE SKIP ROM Command [3Ch]

The TMF0008 supports a high speed mode called the Overdrive mode. The OVERDRIVE SKIP ROM command

sequence starts with the host generating the RESET pulse of at least 480 μs. The device responds with a

PRESENCE pulse. Next, the host continues by issuing the OVERDRIVE SKIP ROM command, 3Ch, in standard

speed. The device now enters Overdrive mode. Make sure all subsequent communication with the target device

are at overdrive speed. The host can bring all the responder devices back to standard speed by issuing a reset

pulse of at least 480 μs.

If the OVERDRIVE SKIP ROM command is issued when there are multiple responder devices on the SDQ

bus. All the responder devices enter Overdrive mode. All subsequent communication addresses a specific

device. This procedure is initiated by issuing a reset pulse at overdrive speed followed by a OVERDRIVE Match

ROM or Search ROM command sequence. This sequence speeds up the time for the search process. If the

OVERDRIVE SKIP ROM command is issued when there are multiple responder devices on the SDQ bus, all the

responder devices begin responding to the subsequent memory command resulting in a bus data collision.

TMF0008

SLVSIV3 – JULY 2025

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