Low-Power LCD Microcontroller

30

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The watchdog timer is controlled through bits in the

WDCN register. Its timeout period can be set to one of

system clocks in its default mode, allowing flexibility to

support different types of applications. The interrupt

occurs 512 system clocks before the reset, allowing the

system to execute an interrupt and place the system in

a known, safe state before the device performs a total

system reset. At 16MHz, watchdog timeout periods can

be programmed from 256µs to 33.5s, depending on the

system clock mode.

Serial Peripherals

The microcontroller incorporates several common seri-

al-peripheral interfaces for interconnection with popular

external devices. Multiple formats provide maximum

flexibility and lower cost when designing a system.

UARTs

Serial interfacing is provided through one (-RBX/-RBX+)

or two (-RAX/-RAX+/-RFX/-RFX+) 8051-style universal

synchronous/asynchronous receiver/transmitters. The

UART allows the device to conveniently communicate

with other RS-232 interface-enabled devices, as well as

PCs and serial modems when paired with an external

RS-232 line driver/receiver. The dual independent

UARTs can communicate simultaneously at different

baud rates with two separate peripherals. The UART

can detect framing errors and indicate the condition

through a user-accessible software bit.

The time base of the serial ports is derived from either a

division of the system clock or the dedicated baud

clock generator. The following table summarizes the

operating characteristics as well as the maximum baud

rate of each mode:

1-Wire Bus Master

The MAXQ2000-RAX/-RAX+/-RFX/-RFX+ include a

Dallas Semiconductor 1-Wire bus master, which commu-

products, through a simple bidirectional signaling

scheme over a single electrical connection. The bus

master provides complete control of the 1-Wire bus and

transmit and receive activities, and generates all timing

and

control

sequences

of

the

1-Wire

bus.

Communication between the CPU and the bus master

is achieved through read/write access of the 1-Wire

master address (OWA) and 1-Wire master data (OWD)

peripheral registers. Detailed operation of the 1-Wire

bus is described in the

Book of iButton Standards

Serial-Peripheral Interface (SPI) Module

The SPI port is a common, high-speed, synchronous

peripheral interface that shifts a bit stream of variable

length and data rate between the microcontroller and

other peripheral devices. The SPI can be used to com-

municate with other microcontrollers, serial shift regis-

ters, or display drivers. Multiple master and slave

modes permit communication with multiple devices in

the same system. Programmable clock frequency,

character lengths, polarity, and error handling enhance

the usefulness of the peripheral. The maximum baud

rate of the SPI interface is 1/2 the system clock for mas-

ter mode operation and 1/8 the system clock for slave

mode operation.

MODE

TYPE

START BITS

DATA BITS

STOP BIT

MAX BAUD RATE

AT 16MHz

Mode 0

Synchronous

N/A

8

N/A

4Mbps

Mode 1

Asynchronous

1

8

1

500kbps

Mode 2

Asynchronous

1

8 + 1

1

500kbps

Mode 3

Asynchronous

1

8 + 1

1

500kbps

iButton is a registered trademark of Dallas Semiconductor Corp., a wholly owned subsidiary of Maxim Integrated Products, Inc.