IZ1990

2

May 2014, Rev. 00

(the open drains will apply the mount AND). In IZ1990 the function ROM Reading may

work with the command byte 33h or 0Fh, which ensures compatibility with the devices

DS1990, which will respond only to the command word 0Fh.

Comparison of ROM [55h] / ROM Skipping [CCh]

As the device IZ1990 contains only 64-bit ROM, the commands COMPARISON OF

ROM and ROM SKIPPING from Protocol 1-Wire are not applied and do not case the

response on the bus, if applied by the master.

Search of ROM [F0h]

When the system is started initially, the bus master may not know the numbers of the

devices, connected to the bus 1-Wire or their 64-bit ROM codes. The ROM search

command enables the bus master to use the exception process, in order to determine the

64-bit ROM codes of all slave devices on the bus. The ROM search process is essentially

repetition of a simple procedure, consisting of three steps: bit reading, reading bit by bit

supplement, and then writing of the required value of the given bit. The bus master

performs this simple step procedure by each ROM bit. After completion of one entire run

the bus master knows the ROM contents of one device. Numbers of the remaining devices

and the codes of their ROMs can be determined by means of the additional runs.

SIGNALIZATION OF BUS 1-WIRE

In order to ensure integrity of data, the device IZ1990 requires the strict observance

of the protocols. The protocol consists of the four types of signalization on one line:

sequence of resetting with the reset pulse and availability pulse, low writing, high writing

and data read-out. With exception of the availability pulse, all these signals are initialed by

the master. The initialization sequence, required for start of any informational exchange

with IZ1990 is indicated in Figure 1. After the reset pulse follows the availability pulse,

which indicates, that the device IZ1990 is ready for reception of the ROM command. The

(releases) the line and switches over to the reception mode. Bus 1-Wire is pulled up to the

status of the HIGH level via the pull-up resistor. After detection of the rising front at the