Parallel Printer interfacing !!

[th3gr8]

Hello All ..
I want to interface a parallel printer with my PIC16F877A (serial printers are not available) .. I googled and found out that i need to connect D0-D7 with any output port of the PIC and need to connect strobe and busy Pin .. Now i am confused about making its code and circuit. I want to know that by directly connecting these pins with my printer, will i be able to print something or do i need any circuit in between them?
and If someone has an example Code and circuit, plz share it ..
Also, can i make it with USB-to-serial interface for a printer having USB port??
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A learner

[Ttelmah]

Sequence is:

Read the BUSY pin. Wait till it goes off.
Write ASCII character to D0 to D7 (just output it).
Turn the STB line on, then off.
Loop back to start, till all characters are sent.

It depends massively on your printer. The basic transmission is the same for all, but simple (old) printers are relatively 'smart', and you only need to send standard text and control characters (line feed, carriage return etc..). A lot of the later 'cheap' printers are completely dumb, and rely on being sent 'raw' binary data, to control the bit patterns on the heads. They relied completely on all the 'work' of generating characters being done in the PC. Too much data for any but the largest PIC's, and completely 'custom' to the particular make of printer.

An interface to a USB printer, would be complex. Most cheap ones do rely on the computer to do all the work, and you would need to implement a USB host. Simplest way (if the printer is not too dumb), is to use an FTDI Vinculum to provide the host. Again if the printer needs anything beyond basic text, serial would have speed issues.

[temtronic]

What Mr. T says is right....very simple code and will hookup to printer directly. I did the same using a 16F84 some years ago.....to allow a serial port from a client's computer to use a parallel port printer.
If your computer sends data slower than the printer prints , you do not need to 'buffer' the data.

hth
jay

[th3gr8]

and if i use a Thermal Printer (with Parallel Port), will the sequence of writing the data be same?
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A learner

[gpsmikey]

If it is a parallel port, the interface should be the same. The printer may need extra processing for graphics or whatever, but the interface you are talking about from a hardware viewpoint is called the "centronics interface" - see here for additional information and links for the interface and timing.
http://en.wikipedia.org/wiki/IEEE_1284

mikey
_________________
mikey
-- you can't have too many gadgets or too much disk space !
old engineering saying: 1+1 = 3 for sufficiently large values of 1 or small values of 3

[th3gr8]

Ok .. but i read somewhere that Centronics interface was used on Old printers etc .. And if i connected the printer with PIC, how much XTAL value would i need? can i work with 4Mhz?? is crystal value very much critical?
_________________
A learner

[Ttelmah]

The parallel printer interface is the Centronics interface. something like 99% of modern PC printers use USB instead. Hence the comment about 'old printers'. There are quite a lot of 'specialist' printers that still use the Centronics interface, just not in the mainstream PC world.

It depends how fast you want to send the data, and how much data you have to send, together with how fast the printer you are talking to is?. Many of the little thermal units can only accept a few hundred characters per second, and this a chip at 4MHz should be able to handle easily. However if you talk to something like a laser printer, and then start sending graphics, rates more like half a million characters per second can be involved to feed the machine properly.

[th3gr8]

Ok.. That helps ..
so now, i want use 10 i/o pins of my PIC and follow the sequence.. do i need to put a resistor on the Data lines (D0-D7) or should i connect it directly?
Sorry for asking such silly questions :( ..
_________________
A learner

[Ttelmah]

For short connections you don't need anything on the data lines. What you do need is a resistor to pull the 'busy' line to the 'busy' state, if the connection is not present. This way the code won't try to send to the printer if it is not there.
On longer cables you'll commonly find termination to help prevent signal 'ringing' at high data rates.

[th3gr8]

[temtronic]

Here's something that worked a few years ago, just needs minor changes to run on 16F877
Jay

[Ttelmah]

If you look at the code, he was using 2400bps, and this was so slow, that Temtronic doesn't even bother about 'busy', being able to assume the printer can always take the next character. Need to think about this if data is arriving faster....

[temtronic]

yup, 2400 baud was what the client's 68K machine's serial port was configured for. I looked at the file...yeesh 10 YEARS ago, time flies.Actual computer($100K when new) was scrapped last year...sigh...
Since most(all) printers have a large 'buffer', handshaking wasn't needed back then.Data from the EVE was less than 500 bytes.
The code as written should be a good start, easy to test(it did work for almost 10 years), easy to modify as required.

Ideally use the 877's hardware UART, CCS's ISR for buffering and a 20MHz xtal.....ideas...

Jay

[gpsmikey]

The actual crystal value is not very critical for the centronics (parallel) interface because it uses the strobe/busy handshake to move data so the crystal frequency is not very critical there (other than lower crystal frequencies mean the processor runs slower). Where the crystal frequency is critical is if you are using the serial port (uart). There, the baud rate is important and it is derived from the crystal so you need to address that issue if you are using the serial port.

mikey
_________________
mikey
-- you can't have too many gadgets or too much disk space !
old engineering saying: 1+1 = 3 for sufficiently large values of 1 or small values of 3

[th3gr8]