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PCD set_open_drain_x()

 
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allenhuffman



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PCD set_open_drain_x()
PostPosted: Tue Sep 28, 2021 3:17 pm     Reply with quote

I found a reference to "set_open_drain_x()" in the General Purpose IO section of the manual, but no details on what x is. I assume it is the port, like other similar calls. Also, header file:

Code:
_bif void set_open_drain_b(unsigned int16 value);
_bif void set_open_drain_c(unsigned int16 value);
_bif void set_open_drain_d(unsigned int16 value);
_bif void set_open_drain_e(unsigned int16 value);
_bif void set_open_drain_f(unsigned int16 value);
_bif void set_open_drain_g(unsigned int16 value);


But what is the value? From this article:

https://simple-circuit.com/pic24fj64gb002-lcd-interfacing-ccs-c/

...they write:

Quote:
For example if I want pin RB0 to be an open-drain output I just write:
set_open_drain_b(1);
For pins RB7, RB8 and RB9 I used:
set_open_drain_b(0x380);
where 0x380 = 896 = 0b0000001110000000


It appears the expected value is a bit pattern. The define for PIN_E4 is 1 0111 0001 0100 so that must not be what it is expecting.

Any tips on where I can find some documentation on this?

Thanks, much.
_________________
Allen C. Huffman, Sub-Etha Software (est. 1990) www.subethasoftware.com
Embedded C, Arduino, MSP430, ESP8266/32, BASIC Stamp and PIC programmer.
www.whywouldyouwanttodothat.com ?
PCM programmer



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PostPosted: Tue Sep 28, 2021 4:21 pm     Reply with quote

Open the CCS manual pdf file. Make sure the PDF file is opened
at the starting page (the cover). Press Ctrl-F to open up a search
box within the Adobe reader. Type in set_open_drain and press
enter. It will highlight the table of contents entry for:
Quote:
set_open_drain_x(value)

Click on that entry with your mouse.

It will take you to the entry for set_open_drain_x(value) in the text.
That entry tells you what you need to know about the parameter.

CCS manual:
http://www.ccsinfo.com/downloads.php
Ttelmah



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PostPosted: Wed Sep 29, 2021 12:45 am     Reply with quote

and seriously, just use binary. It makes things so much easier.
So for B7, B8 & B9:
set_open_drain_b(0b0000001110000000);

While for E4:
set_open_drain_e(0b0000000000010000);

Much easier to understand what pin is involved.

Understand this only applies on chips that have the ability to set pins to
open_drain mode.
allenhuffman



Joined: 17 Jun 2019
Posts: 498
Location: Des Moines, Iowa, USA

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PostPosted: Wed Sep 29, 2021 8:22 am     Reply with quote

Ttelmah wrote:
and seriously, just use binary. It makes things so much easier.
So for B7, B8 & B9:
set_open_drain_b(0b0000001110000000);

While for E4:
set_open_drain_e(0b0000000000010000);

Much easier to understand what pin is involved.

Understand this only applies on chips that have the ability to set pins to
open_drain mode.


Looks like another case of "not in the help file."

I noticed the bits, but what are the high bits in the #defines? 5904 for bit four, but what do the 59 bits mean?
_________________
Allen C. Huffman, Sub-Etha Software (est. 1990) www.subethasoftware.com
Embedded C, Arduino, MSP430, ESP8266/32, BASIC Stamp and PIC programmer.
www.whywouldyouwanttodothat.com ?
Ttelmah



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Posts: 17485

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PostPosted: Wed Sep 29, 2021 9:34 am     Reply with quote

What #defines?.

I think you are confusing bit numbers with port masks.
The #define for PIN_E4, is the value to be fed to things like the output_high
and output_low functions. Nothing to do with a port mask for things like
this, and TRIS.

Functions that have _a, _b etc. at the end are just talking directly to
the registers associated with the single port. So 'output_b', just talks
to the whole of port B. It expects to receive a byte value to send to the port.
(or int16 for PCD).
The TRIS functions, and this open_drain function, again talk to the registers
for a single port, and expect a byte (or int16 for PCD) value with each
bit corresponding directly to the bit in the port.
This is completely separate from things like output_high, and output_low,
which expect to receive a value that is actually the register address of the
output register (*8 for PCM/PCH, and *16 for PCD), plus the bit number
to operate in this register.

The manual makes this very clear. If you look at the entry for the
open_drain function, it says:
Quote:

Parameters:
value – is an 8-bit int with each bit representing a bit of the I/O port.

[PCD] value – is a 16-bit int with each bit representing a bit of the I/O port.



While if you look as 'output_high', it says:
Quote:

Parameters:
The PIN could also be a variable. The variable must have a value equal to one of the constants (like PIN_A1) to work properly. The tristate register is updated unless the FAST_IO mode is set on port A. Note that doing I/O with a variable instead of a constant will take much longer time.

[PCD] pin to write to. Pins are defined in the devices .h file. The actual value is a bit address. For example, port a (byte 0x2C2) bit 3 would have a value of 0x2C2*8+3 or 5651. This is defined as follows: #DEFINE PIN_A3 5651.


You must not mix the two types of value.

The open_drain function is a port_wide function, not a function that works
or accepts single bit defines.
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