Raspberry Pi Serial Port running Pico

Hello,

This is my first post, so I hope that I’ve put it in the right place.

I’m running Pico on a Raspberry Pi and would like to use serial communication to control a Poloku Serial Servo controller.
In it’s simplest mode, the servo controller requires 8N1 serial input at logic level (0-5v) which the Pi hardware can deliver.
Commands are issued in three bytes, the first being 255 (a fixed number to initiate action by the board) followed by a servo number (0-15), then a servo position (0-254).

However, I’m struggling to get Basic to persuade the Pi to send any serial data. OS_SerialOp doesn’t appear to be having any effect.

Could someone post an example piece of code that I can copy or at least point me in the right direction?

Many thanks

Neil

As the serial port is sometimes used as a debug-output for porting, it might be that this port is not accessible from pico, but I am not sure.
you could listen with an appropriate cable during boot.
Another thing could be the choice of cable – 1:1 or Null-Modem. Have you checked this?

About availability, ROOL should know – anybody?

The serial port is not implemented in RISC OS on the Pi yet and does, as you say, output debug info. This is normally only at boot, so the hardware could be used at other times. To do so you could use This
and just use the PiSerial module from !SerialDev.Modules.PiSerial.Modules and read the included BlockDrvs helpfile for the SWIs available.

The serial port on the Pi is only 3v3, so you need to add an interface chip to get to 5V.

Tank – I have not used RISCOS since about 1993 so I am rusty, I have tried to get the Pi serial port working. What do you mean by “use the PiSerial module from !SerialDev.Modules.PiSerial.Modules” – what am I supposed to do with it?
Loopback runs through with no errors
I have done RMload PiSerial as in loopback then PiSerial_ResetUART then set up the speed but using PiSerial_TX nothing comes out of the TxPin. After running loopback do the registers need resetting to nonloopback use for normal Tx Rx to work?

I never try it with my Pi but for xM, Panda and MX6 I use the blockdriver and “merge in” the right serial module… so PiSerial for the RPi I think.

Raik – I take it you are familiar with Tank’s module, isn’t that what RMload PiSerial does?

Here’s a demo program I have (PiSerialTerm.zip) which works on a pi and creates a simple terminal in a taskwindow using the serial block drivers. Unfortunately
you are not using the desktop so to get it to work you will have to alter it (eg stop RunTerminal running Terminal in a taskwindow) but it should work singletasking other than that.

Colin – Thank you for the PiSerialTerm link. When I first tried it, it didn’t work but the next day it did and so did my code. Memo to self – test hardware after a power-on boot not after a reset.

Tank – I am using PiSerial to send commands to a Zero-2 robot which I created back in 1984. The Pi is fitted with a Max 3232 and D9 and the system checked by sending commands to WindowsXP running Bray’s Terminal.
Two weird things happen.
1 – if I put my program in !Configure,Boot,Run then it runs on reboot but the baudrate is incorrect. The boot message comes through at 115200 baud.
My program after
*RMEnsure PISerial 0.00 RMLoad $.PISerial
sets the baud rate to 4800 with
SYS “PiSerial_Speed”,,4800.
then sends commands
However characters received by the PC are at no standard baud rate.
If I quit my program and rerun it then the baudrate is set correctly to 4800.

2 – it seems to me SYS “PiSerial_TX”,,byte% doesn’t add to bytes in the buffer but overwrites anything still there.
*RMEsure PISerial 0.00 RMLoad $.PISerial
SYS “PiSerial_ResetUART”
SYS “PiSerial_Speed”,,4800
WHILE 1=1
FOR C%=0 TO 150
SYS “PiSerial_TX”,,“A” :PRINT “A”;
NEXT C%
FOR C%=0 TO 150
SYS “PiSerial_TX”,,“B” :PRINT “B”;
NEXT C%
ENDWHILE
END
prints 150 “A” then 150 “B” in the task screen (single task or task window) but the PC only receives
“AAAAAAABBBBBBBAAAAAAABBBBBBB…”

Am I doing something wrong?

I don’t think there is any handshaking so stuff will get lost?

David, I have tested the module on my setup, and it also has this problem talking to a PC…
Strange that it didn’t show up before.
The problem was FIFO related.
So fixed that. Please send me your email and I’ll send you the module to test. webmaster@tankstage.co.uk

Chris – it is impossible for Zero2 to loose bytes since the outputs from the UART directly drive logic electronics. The PC has a large serial buffer which at 4800 baud when the data is simply printed to the screen by a Terminal program is virtually impossible to fill and it would never repeatedly ‘loose’ 143 bytes.

Tank – Thank you for the speedy reply, I have emailed you.