RS232 interface for general-purpose bus

This is an RS232 extension card for the Universal I/O Interface for IBM PCs.The circuit is based on the COM81C17 UART (universal asynchronous receiver jtransmitter) from Standard Microsystem Corporation (SMC). This IC has an on-board programmable baud rate generator, which obtains its clock from a quartz crystal oscillator built around three gates in the 74HCT04 package.