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redrok

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Joined: 15/09/2014
Location: United States
Posts: 209

Posted: 06:52am 14 Jan 2015

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Hi All;

I've been experimenting with IEEE485/RS485 interfaces between a pair of uMiteIIs on a plugboard.
1. Using EXAR SP485E interface chips. These seem to be working fine.
2. Using COM1:
3. /DE is inverted to DE using a 2N7000 MOSFET.
4. /RE is grounded, (Although I have also tried connecting /RE to DE).

I'm not a "Software guy", pretty good at hardware though.
My "test goal" is to have each uMiteII read 2 i2c RTC clocks and compare them. The clock stuff works perfectly.
I'm now just attempting to just send and catch individual characters.
The master program just spits out 1 character every second.

'RS485ClockMaster1.bas
Start:
option autorun on
cpu 40
'OPEN "COMn: baud, buf, int, intlevel, DE, 9BIT, INV, OC, S2"
open "com1: 300,DE" AS #1
setpin 6, DOUT
Again:
PRINT #1, CHR$(65);
pin(6)=1:pause 500:pin(6)=0:pause 500
GoTo Again

The slave program should catch each character and send them to the console.

'RS485ClockSlave1.bas
Start:
option AUTORUN on
cpu 40
'OPEN "COMn: baud, buf, int, intlevel, DE, 9BIT, INV, OC, S2
open "COM1: 300, DE" AS #1
setpin 6, DOUT
Again:
IF LOC(1) >= 1 THEN ' check that we have at least one byte
pin(6)=1
A$ = INPUT$(1,1)
' Send the character to the console
print "<Lenth of A$=";len(A$);"><ASCII Code of A$=";ASC(A$);"><A$=";chr$(34);A$;chr$(34);">"
ENDIF
pin(6)=0
GoTo Again

However, it only sends this once and gets stuck.

> RUN
<Lenth of A$= 1><ASCII Code of A$= 0><A$="

This happens only once after the code is flashed.
I get nothing after a reset or a "RUN" command, it's just stuck.

Are there any "Running" code examples?
Something I can use to at least get things running?
The example in the manual is just a code snippet.

redrok

WhiteWizzard
Guru

Joined: 05/04/2013
Location: United Kingdom
Posts: 2932

Posted: 08:23am 14 Jan 2015

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Hi redrok,

A couple of questions:

1> What is pin 6 connected to on the master and slave? (An LED maybe to act as a visual indicator??)
2> The print command on the Master ends in a semicolon. Could this be impacting on any other hardware (by it suppressing the CR & LF characters?
3> Is there any way you can test this without DE (to help eliminate things)?

WW

WhiteWizzard
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Joined: 05/04/2013
Location: United Kingdom
Posts: 2932

Posted: 08:38am 14 Jan 2015

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Ok - been reading more about this . . .

One bit in the manual that stands out with your symptoms:

Quote
MMBasic does not check that data is printed or read to/from the COM port in pairs. If your program inadvertently sends or reads a single character it will disrupt all subsequent communications.

Have you tried using the example in the manual with 9bits (and byte pairs)?

WWEdited by WhiteWizzard 2015-01-15

redrok

Senior Member

Joined: 15/09/2014
Location: United States
Posts: 209

Posted: 04:01am 15 Jan 2015

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Hi WhiteWizzard;
1. Yes, pin 6 is just an experimental LED indicator.
2. Apparently the tools I'm using, "MM Edit" & "TeraTerm", don't mind not having terminators. At least I haven't seen any problems.
3. I did try disabling DE, made DE high, to make sure the SP485E interface chips were working properly. They were apparently working well.
4. I did try the 9 bit method but that didn't work either.

But I did finally solve the problem. Actually 2 problems.
A. I had to add the "INV" invert parameter on both ends.
B. The master was over running the slave. Adding a small pause in the master allows the slave to process the characters it catches.

Ok, now that I have the physical layer running, at least in one direction, I can go on to the data link layer with addressing and data framing.

One question though, Why do I need the "Invert" parameter?
It would seem that if both ends are the same polarity the data would get through.
Apparently not true, but why?

redrok

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