NS16550A
NS16550A is UART Design and Application Considerations manufactured by National Semiconductor.
features while maintaining software patibility These development paths have been brought together in a new UART from National Semiconductor designated the NS16550A The NS16550A has all of the registers of its two predecessor parts (INS8250 and NS16450) so it can run all existing IBM PC XT AT RT and patible serial port software In addition it has a programmable mode which incorporates new high-performance features
Of course all of these advanced features are useful in any asynchronous serial munications application regardless of the host architecture The reader is assumed to be familiar with the standard features of the NS16450 so this paper will concentrate mainly on the new features of the NS16550A If the reader is unfamiliar with these UARTs it is advisable to start by reading their data sheets The first section reviews some of the design considerations and the operation of the NS16550A advanced features
The second section shows an NS16550A initialization routine written in 80286 assembly code with an explanation of the routine The third section gives a detailed example of munications drivers written to interface two NS16550As on individual boards These drivers are written for use with National Semiconductor’s DB32032 evaluation boards but can be ported to any NS32032-based system containing an NS32202 (ICU)
National Semiconductor Application Note 491 Martin S Michael Daniel G Durich July 1987
The CPU is usually much faster than the UART at transferring data A high speed CPU could transfer a byte of data to from the UART in a minimum of 280 ns The UART would take over 1800 times longer to transmit receive this data serially if it were operating at 19 2 kbaud 2 There is a finite amount of wasted CPU time due to software overhead when stopping its current task to service the UART (context switching overhead) 3 The CPU may be required to...
