PIC18f4520 and e8051 uart mode - help needed

silelis · Posted: Mon Oct 02, 2017 10:26 am

Hello,

I have to communicate with my PIC (20MHz) with 8051 "like" mcu. It is UART transmission. Exactly it is au7860 mcu and it's communication protocol is here.

Generally it is:

temtronic · Posted: Wed Oct 04, 2017 5:29 am

Overall this is just 'regular' serial communications, so no need to reverse the bits or those cmd bytes. The 'device' needs the data sent in the order you show.

NOW the big 'issue' is the hardware. That PDF is just the commands and doesn't explain the interface connections.
Typically , most 'devices' today are 3 volts so it's best to select a 3 volt PIC. Any( most ?) with L in them ( ie: 16LF84 ) are designed to run on 3 volts. Some PICs, like the 18F46K22 are designed to run on 5 or 3 volts. You don't say which PIC you're using...that's an important detail!

UART could mean 'TTL' signals. The datasheet will explain what is required. Hopefully it's as simple as connecting the PIC's XMT pin to the MP3's RCV pin, and the PIC's RCV pin to the MP3's XMT pin.

To begin, cut code to send a SIMPLE command to the device and display the result either to a local LCD or PC terminal program. Confirm that works, then test other commands. One step at a time...wins !

Jay

silelis · Posted: Wed Oct 04, 2017 5:42 am

The PIC is 18f4520 but the mp3 hardware is secured with resistors provided voltage drop on au7860 UART port. MP3 hardware developer assure that it is enough but in my final hardware I will use BSS138 logic level converter.

temtronic · Posted: Wed Oct 04, 2017 6:37 am

I downloaded the datasheet for the 4520 and it'd be easier for you to just order/use the 18LF4520 PIC. That way NO additional parts needed between PIC and MP3 device !
Also then you only need a 3 volt power supply.

Jay

silelis · Posted: Wed Oct 04, 2017 7:44 am

Where can I find this pic18LF4520 datasheet I can see only pic18F4520 at the net??

newguy · Joined: 24 Jun 2004 Posts: 1909

It's the same data sheet. Only difference lies in acceptable power supply voltage range, and there is usually also a difference in maximum clock speed vs power supply voltage. Those differences are spelled out in the electrical specifications chapter of the data sheet.

silelis · Posted: Wed Oct 04, 2017 7:51 am

Ohhh I see.

Any in this LF version is possible to supply it with 5V0 and to set it (in come register) that outputs are 3V3??

Asking because some fo my devices are supplied with 5V0. Or it is like this that which power supply mcu this voltage is on outputs??

silelis · Posted: Wed Oct 04, 2017 7:59 am

And how is it with cpu speed?

Do I understand it correctly that external quartz is the same (in my example 20 MHz) but only cpu speed changes?

newguy · Joined: 24 Jun 2004 Posts: 1909

With any PIC I'm aware of, it's not possible to have them output a normal digital output voltage that is different from their power supply. So 5V supply to your PIC means that a logic high will be 5V. There are, however, PICs that are meant to run at 3.3V but will tolerate 5V inputs. dsPICs in particular have this capability on some of their ports/pins, but not all.

Regarding your speed/crystal question, look at pages 322 and 323 of the data sheet. For the "F" parts, they'll run at a speed of up to 25MHz at power supply voltages of 4.2V and above. As you'll then see on page 323, for "LF" parts, their maximum speed depends on power supply voltage. The equation for the line is given below the graph.