The result is a 16-bit word (low byte transmitted first,

high byte second) that contains the register that

caused ALERT to assert. An error (8103h) is returned

when there is no active ALERT.

RESET

The MAX6621 features a power-on reset (POR), bus

lockout reset, and a reset input (RESET). The power-on

after power-up.

Bus Lockout Timeout Reset

greater than 20ms, the MAX6621 asserts the internal

bus lockup reset that restarts itself in the default startup

condition.

The MAX6621 features a RESET input that allows users

to directly reset to the default startup conditions. Pull

RESET low for a minimum of 10ns for a valid reset. The

MAX6621 requires 100μs to be accessible after RESET

has been asserted.

Version Information Command

Table 18 shows the command to read the firmware version.

The result is a 16-bit word (low byte transmitted first,

high byte second), e.g., 0100h for the MAX6621 firmware

version 1.0.

Serial Interface

The MAX6621 operates as a slave that sends and

face. The interface uses a serial-data line (SDA) and a

serial-clock line (SCL) to achieve bidirectional commu-

nication between master and slave. A master (typically

a microcontroller) initiates all data transfers to and from

the MAX6621 and generates the SCL clock that syn-

chronizes the data transfer (Figure 5).

The MAX6621 SCL and SDA lines operate as both

inputs and open-drain outputs. A pullup resistor is

required on SCL and SDA.

Each transmission consists of a START condition sent

by a master, followed by the MAX6621 7-bit slave

address, plus an R/W bit, one or more data bytes, and

finally a STOP condition (Figure 6). To write to a

MAX6621 register, a write transmission consists of a

START condition, followed by the MAX6621 7-bit slave

address plus R/W = 0, a register address byte, one

data byte, and finally a STOP condition. To read from a

MAX6621 register, a combined write and read trans-

missions are required. The first write transmission con-

sists of a START condition, followed by the MAX6621

7-bit slave address plus R/W = 0, a register address

byte, and finally a STOP condition that sets the register

to be read. The second read transmission consists of a

START condition, followed by the MAX6621 7-bit slave

address plus R/W = 1, one or more data bytes, and

finally a STOP condition that reads the data from the

______________________________________________________________________________________

13

COMMAND

DESCRIPTION

TYPE

RESULT

09h

Get firmware

version

ReadWord

16 bit word

Table 18. Firmware Command

SDA

SCL

START

CONDITION

STOP

CONDITION

REPEATED START

CONDITION

START

CONDITION

Figure 5. 2-Wire Serial-Interface Timing Details