UART.TXT last updated by Roedy Green 1996 Jan 17

PURPOSE
*******

UART lets you check that your COM ports are configured
correctly, with the standard hex port address e.g. COM4:
should be at 2e8, and with the standard IRQ, e.g. COM4
should be IRQ 3.  It also tells you what type of UART chip
you have, usually the old fashioned unbuffered 8250 or the
newer fifo buffered 16450 that is needed for Windows and
OS/2.

It expects this pattern COM1: COM2: COM3: COM4:
                  port:  378   2f8   3e8   2e8
                   irq:    4     3     4     3

USAGE
*****

Under vanilla DOS, just run UART once for each of your COM
ports.  e.g.

UART COM1:
UART COM2:
UART COM3:
UART COM4:

You can also use UART in a BAT file and switch on the
errorlevel it returns.

  UART COM1:
  If Errorlevel 5 GoTo SyntaxError
  If Errorlevel 4 GoTo PS2TYPE3
  If ErrorLevel 3 GoTo AT16550FIFO
  If ErrorLevel 2 GoTo AT16450
  If ErrorLevel 1 GoTo XT8250
  If ErrorLevel 0 GoTo NoSuchPort

UART by itself is considered a syntax error and generates a
usage message.

Sets errorlevel to type of UART detected.

LOOPBACK PLUG
*************

Sometimes UART may suggest using a LOOPBACK plug to get
more accurate results.  Peter Norton nows sells such plugs
to accompany his utilities.  They also come with diagnostic
programs such as QAPlus or CheckIt.

If you want to roll your own they look like this:
9 pin serial                    25 pin serial
02 - 03                         02 - 03
07 - 08                         04 - 04
06 - 01 - 04 - 09               06 - 08 - 20 - 22

TECHNICAL NOTES
***************

The code is based on the MASM routines on page 364 Of PC
Magazine May 26, 1992.

In DESQview often ports COM1: and COM2: are not accessible.  You
must have access priviledge in your PIF.  If UART says there are
no ports, the simplest thing to do is run under pure DOS
without DESQview.

Under OS/2, virtualization makes all com ports look like
8250s, so it is best to run under DOS.

UART supports only COM1: .. COM4:.  It looks in BIOS Table
to find the corresponding physical addresses.

It expects this pattern COM1: COM2: COM3: COM4:
                  port:  378   2f8   3e8   2e8
                   irq:    4     3     4     3
                   int:    C     B     C     B

If, for example, COM1: has port 2f8, then irq 3 would be
anticipated and its interrupts would be fielded on int vector B.

Port has precedence over com port number in determining irq.  So
for example, if someone removed your modem on COM2: without
reconfiguring your machine, DOS would slide COM3: down to COM2:
and COM4: down to COM3:.  This is just asking for trouble, since
then you have a pattern COM2: = 3e8 = irq 4.  UART treats this
as an error, even though some programs will survive it.

How UART Works
**************

If you are very curious, your best bet is to read the comments
in the source code UART.ASM. Even if you don't understand
assembler, you still might be able to learn a fair bit.

The code to discriminate chip types depends on detecting the
presence of the scratch register, added after the 8250.  Then we
check for FIFO buffers, added with the 16550AF.  Then we check
for the enhanced register and DMA added with the IBM type 3.

To check the IRQ we simple send a NULL character to the port,
then wait on the CORRECT IRQ for an interrupt.  If we get
exactly one, we are golden.

Five things can then happen:

1. device accepts the char, and we get a Xmit buffer empty interrupt.
   This is the "nice" case.  A loopback plug will also simulate this case.

2. device keeps CTS low, so char never goes out.  We never get an int.
   This is the case for example if a serial mouse is attached that
   has not been activated.  This is a "nasty" case.

3. device is powered off or missing. Then we get a line status
   interrupt instead.  This is the normal case when nothing at all
   is connected to the port.  We can still tell that the irq is correct.

4. IRQ not set properly.  We see no interrupt.  This is the error UART
   was designed to detect.

5. Some other device is also using same IRQ.  Then we may see spurious
   extra interrupts from that device.  Again we can report the problem
   to the user.

MONEY
*****

UART is free. We put out a suite of similar utilities, a
mixture of shareware and freeware.  If you would like
almost the entire shebang of 70 odd utilities with source,
preregistered, please send a cheque for $20 US or Canadian
to:

CMP UTILITIES
Canadian Mind Products
#601 - 1330 Burrard Street
Vancouver, BC CANADA V6Z 2B8

If you do that, I will be willing to give you phone support
for UART as well. We are too small right now to accept
credit cards.

Projects in the works are described in my resume, Roedy.txt

GROVELLING

I have AIDS.  I have been HIV+ since 1985.  I was too ill
to continue working, and left my job in December 1994.  I
have been living on my savings ever since.  They are just
about exhausted.  One of the medications (Cipro) I take
costs $125 per prescription.  I have not been able to
afford it of late.

I have been supporting a dozen foster kids in the third
world.  I don't want to abandon them.  Receiving a
registration for the CMP utilities in the mail is
most welcome.

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