TLC9320

National Semiconductor

Application Note 493

Martin S Michael

April 1989

A Comparison of the

INS8250 NS16450 and

NS16550AF Series of

UARTs

National currently produces seven versions of the INS8250

UART Functionally these parts appear to be the same

however there are differences that the designer and pur-

chaser need to understand For each version this docu-

ment provides a brief overview of their distinct characteris-

tics a detailed function and timing section a discussion of

software compatibility issues and the AC timing parameters

10 Part Summary

The seven versions currently produced are designated

INS8250 INS8250-B INS8250A NS16450 INS82C50A

NS16C450 and NS16550AF These devices are grouped

below by process type

XMOS DEVICES

1 INS8250 This is the original version produced by Nation-

al It is the same part as the INS8250-B but with faster

CPU bus timings

2 INS8250-B This is the slower speed (CPU bus timing)

version of the INS8250 It is used by many popular 8088-

based microcomputers

3 INS8250A This is a revision of the INS8250 using the

more advanced XMOS process The INS8250A is better

than the aforementioned parts due to the redesign (com-

pare section 20 to 30) and the following process charac-

teristicscloser threshold voltage control more reliably

implemented process topography and finer control over

the active area critical dimensions XMOS and CMOS

parts should be used for all new designs This part is

used in many popular 8086-based microcomputers

4 NS16450 This is the faster speed (CPU bus timing) ver-

sion of the INS8250A It is used by many popular 80286-

based microcomputers

5 NS16550AF This is the newest member of the UART

family It powers-up in the NS16450 mode and is com-

pletely compatible with all software written for the

NS16450 It has advanced features such as on-board

FIFOs a DMA interface faster CPU bus timings and a

much higher maximum baud rate than the NS16450 The

NS16550AF should be used for all new non-CMOS de-

signs including those that were originally done with the

NS16550 It is used in recent versions of popular 80286-

based 80386-based and ROMP-based microcomputers

Software written for the NS16550 is completely compati-

ble with the NS16550AF Section 50 describes how the

software can distinguish between the NS16550 and the

NS16550AF

6 NS16550 This part powers-up in the NS16450 mode and

is completely compatible with all software written for the

NS16450 It has advanced features such as a DMA inter-

face The on-board FIFOs are essentially non-functional

This part was issued on a limited basis Any user that

wants this part should order the NS16550AF Section 50

describes the differences between the NS16550 and the

NS16550AF in detail

CMOS DEVICES

1 INS82C50A This is a CMOS version of the INS8250A It

functions identically and for most AC parameters has the

same timing specification as the INS8250A (see Section

40) It draws approximately 110 (10 mA) of the maxi-

mum operating current of the INS8250A

2 NS16C450 This is a CMOS version of the NS16450 It

functions identically and for most AC parameters has the

same timing specification as the NS16450 (see Section

40) It draws approximately 112 (10 mA) of the maxi-

mum operating current of the NS16450

Note

The XMOS and CMOS UARTs are not plug-in replacements for the

INS8250INS8250-B when used with ICUs that are in the popular

edge-triggered configuration However there are easily implement-

ed adjustments to the driving software or associated hardware that

will allow these parts to be a plug-in replacement (see Section

60)

TLC9320 – 1

FIGURE 1 Connection Diagram

20 INS8250 and INS8250-B

Functional Considerations

Designers using these parts should be aware of the follow-

ing considerations

1 When multiple interrupts are pending the interrupt line

(INTR) pulses low after each interrupt instead of remain-

ing high continuously

Recommendation This will not cause problems in normal

operation however it is a condition necessary for com-

patibility in some popular 8086- and 80286-based micro-

computers that use an edge-triggered ICU (see Section

60)

C1995 National Semiconductor Corporation

RRD-B30M105Printed in U S A