Serial Three Bit Port – firmware version 1.1


Quantity Pricing

The following are the unit prices, as you vary the quantity purchased:






All prices are in Canadian dollars. We use the total number purchased (ELM621P + ELM621SM) for the calculation.


The ELM621 is a serially controlled, three bit parallel I/O port in an 8 pin package. The high level of integration employed means that very few external components are required in order to construct a fully functional circuit with this IC.

The ELM621 offers several convenient features that many users will appreciate. The provision of a 16 byte buffer allows commands to be chained and executed sequentially with one key stroke. The controllable pullup resistor on the bit 3 port pin is particularly helpful when interfacing to mechanical switches, while the ability to control character echo reduces overhead while operating under computer control. Naturally, individual as well as simultaneous read, set, clear and toggle commands are also supported.

All communications with this device are via a standard 9600 baud serial connection, using AT style commands. No special characters are required, so that virtually any terminal program can be used with the ELM621. More advanced users will be interested in operating this device under computer program control – simply a matter of writing to and reading from the device.


  • Home automation monitoring and control
  • Robotics
  • Security monitoring
  • IC programmers


  • Low power CMOS design – typically 1mA
  • High speed (9600 baud) RS232 communications
  • Standard ASCII commands and responses
  • 16 byte receive buffer
  • Switchable pullup resistance
  • Minimum of external components required
  • External reset input
  • High current drive outputs – up to 25 mA

Connection Diagram

( PDIP or SOIC, top view )
ELM621 connection diagram

Block Diagram

ELM621 block diagram


The ELM621 data sheet (ver A, 38K):

pdf icon

Related Products

We currently offer no similar devices.