responder devices by driving the SDQ bus low for at least 480 μs. The PRESENCE pulse lets the host know that

there are one or more responder devices on the SDQ bus.

6.5.3 ROM Commands

After the host detects the presence of one or more responder devices on the SDQ bus, the host can send an

8-bit ROM function commands shown in Figure 6-6. This section describes the scenarios where each of the

ROM command can be issued. See Figure 6-6 for list of these commands.

6.5.3.1 READ ROM Command [33h]

The READ ROM command sequence (shown in Figure 6-7) 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 READ

ROM command, 33h, and then reads back the 56-bit Family code and serial number followed by the 8-bit CRC

using the READ signaling (see the READ and WRITE signals section) during the data frame. The READ ROM

command can be issued by the host only if there is a single responder device on the SDQ bus. If the host issues

the command when there are more than 1 responder device on the SDQ bus, then data collision occurs because

all the responder devices try to respond to the host. The host can identify the data collision by comparing the

CRC from the READ ROM sequence with the computed CRC, which results in a mismatch.

0

1

1

0

0

0

1

1

CRC (1 BYTE)

Reset

and

Presence

Signals

Read ROM (33h)

Family Code and Identification

Number (7 BYTES)

Figure 6-7. READ ROM Sequence

6.5.3.2 Match ROM Command [55h]

When there are multiple responder devices on the bus, the Match ROM command, 55h, is used by the host to

select a specific responder device when the family code and identification number is known. The host issues the

Match ROM command followed by the family code, serial number, and the CRC byte. The responder device that

matches the 64-bit serial ID is selected and available to perform subsequent memory function commands. The

MATCH ROM command can also be used with a single responder device on the bus.

1

1

0

0

0

1

1

CRC (1 BYTE)

0

Reset

and

Presence

Signals

Match ROM (55h)

Family Code and Identification

Number (7 BYTES)

Figure 6-8. Match ROM Sequence

6.5.3.3 SKIP ROM Command [CCh]

The SKIP ROM command sequence (shown in Figure 6-9) is the fastest sequence that allows the host to begin

transacting with the responder device. The Skip ROM command, CCh, allows the host to access the memory

functions without issuing the 64-bit serial ID. The Skip ROM command is directly followed by a memory function

command. The SKIP ROM command is only issued with one device present on the SDQ bus. If the 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 data collision on the bus.

www.ti.com

TMF0008

SLVSIV3 – JULY 2025

Copyright © 2025 Texas Instruments Incorporated

Submit Document Feedback

13

Product Folder Links: TMF0008