Product category: Analogue and Mixed Signal ICs
News Release from: Texas Instruments (April 2001-March 2006) | Subject: SN74LV8153
Edited by the Electronicstalk Editorial Team on 6 October 2004
Output expander aids flexible interfacing
The SN74LV8153 8bit output expander provides an alternative to monitoring and controlling the inputs and outputs of a system's microcontroller or microprocessor
Designed to provide an alternative to monitoring and controlling the inputs and outputs of a system's microcontroller or microprocessor, the SN74LV8153 8bit output expander joins TI's existing PCF8574 and PCF8574A I/O expansion devices. These TI expanders offer a viable method of accessing a parallel bus and a practical means of interfacing with different peripheral devices.
This article was originally published on Electronicstalk on 6 October 2004 at 8.00am (UK)
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A limiting factor in determining total system functionality in microcontroller- or microprocessor-based equipment is the number of general purpose inputs and outputs (GPIOs) provided on the processor.
To maintain a reasonable average selling price, the microcontroller/microprocessor vendor must keep the number of GPIOs to an amount suitable for the most common tasks (memory interface, dedicated host-to-peripheral interfaces etc), envisioned for its target applications.
It is then up to the system designer to best manage the GPIO resources after selecting the processor for a particular system.
As virtually all modern processors feature dedicated UARTs and I2C interfaces separate from the pool of general-purpose pins, they can use UART and I2C controlled expanders to add system functionality without sacrificing GPIOs.
The LV8153 and PCF8574/PCF8574A provide this expansion through connection to an existing UART or I2C bus, respectively.
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By using expanders such as the LV8153, PCF8574 or PCF8574A system designers can incorporate additional processor-controlled outputs (LV8153) or inputs/outputs (PCF8574/PCF8574A) in their system without using general-purpose input/output pins.
The new SN74LV8153 UART-controlled 8bit output expander has a low voltage (3 to 5.5V) supply rail for interfacing with the microprocessor and a wider voltage (3 to 12V) supply rail for driving its outputs; thus making this device ideal for interfacing between low voltage processors and higher voltage peripherals.
Additionally, the LV8153 outputs can be configured as either open-collector or push-pull for easy connection to actively-driven and open-drain buses.
In the open-drain mode, the outputs are capable of sinking 40mA ideal for high drive applications such as LED control.
Three user selectable address pins allow for up to eight SN74LV8153s to be individually controlled from the same UART.
TI's PCF8574 and PCF8574A are I2C controlled 8bit general-purpose remote input/output expanders which operate from supply voltages between 2.5V to 6V.
These devices have low standby current consumption (10uA maximum) and feature latched outputs with 25mA current sinking capability suitable for driving LEDs.
Both the PCF8574 and PCF8574A use the standard 8bit (7bit address followed by a read/write bit) I2C protocol.
The four most significant address bits are preset internally (0100 for the PCF8474 and 0111 for the PCF8574A) and the three least significant address bits are user selectable via the hardware address pins.
This combination of predetermined and user-selectable addressing allows a total of 16 remote I/O expanders to be connected to the same I2C bus without address conflicts while providing a total of 128 additional I/Os for the processor.
The SN74LV8153 is offered in the industry standard TSSOP (PW) package and is readily available to sample.
Budgetary pricing for this device is set at $1.21 in quantities of 1000.
The PCF8574 and the PCF8574A are offered in the space saving, low profile 20-pin QFN (RGY) package along with the TVSOP (DGV) and TSSOP (PW) packaging.
Both the devices are currently available to sample with budgetary pricing for both set at $1.76 in quantities of 1000.
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