RS232 interface limitations on CM5/510
RS232 interface limitations on CM5/510
by PedroR
Mon Jun 20, 2011 4:13 pm
Hi all
While discussing a project here at RobSavvy we came across a post by the ActuatedCharacter blog (a project that RoboSavvy is part of) where the RS232 interface of the CM5 has been explored.
Interestingly enough the older CM5s use a HIN232 chip and newer CM5 s as well as the CM510 use a MAX202.
Both chips have a theoritical maximum speed limit of about 120kbps which means you won't be able to ever use the CM5/510 as a High Speed bridge to the servo bus (using a custom firmware).
Their findings are quite interesting including findings that you're able to overclock the chips beyond the specifications.
The article is here http://actuated.wordpress.com/2010/09/2 ... mitations/
The AVR processor on these boards has serial UART ports at 5V standard (TTL/CMOS). To do the step-up voltage conversion, CM5 uses the HIN232 chip and CM510 uses the MAX202C chip. Unfortunately these chips can only drive 125kbps and not 1mbps as we need.
To analyze the RS232 communications we have used the Saleae Logic Analyzer, connected to the lines between the Atmega microcontroller and the RS232 Transceiver (HIN232). You can see the probes in the following picture.
Even though the chips are rated with 125Kbps limitation, we manage to get stable communication at 500Kbps but only in one direction : CM5 to PC. In the picture below you can see the sequence of bytes sent from the CM5 to the Roboard and perfectly captured.
Pedro.
While discussing a project here at RobSavvy we came across a post by the ActuatedCharacter blog (a project that RoboSavvy is part of) where the RS232 interface of the CM5 has been explored.
Interestingly enough the older CM5s use a HIN232 chip and newer CM5 s as well as the CM510 use a MAX202.
Both chips have a theoritical maximum speed limit of about 120kbps which means you won't be able to ever use the CM5/510 as a High Speed bridge to the servo bus (using a custom firmware).
Their findings are quite interesting including findings that you're able to overclock the chips beyond the specifications.
The article is here http://actuated.wordpress.com/2010/09/2 ... mitations/
The AVR processor on these boards has serial UART ports at 5V standard (TTL/CMOS). To do the step-up voltage conversion, CM5 uses the HIN232 chip and CM510 uses the MAX202C chip. Unfortunately these chips can only drive 125kbps and not 1mbps as we need.
To analyze the RS232 communications we have used the Saleae Logic Analyzer, connected to the lines between the Atmega microcontroller and the RS232 Transceiver (HIN232). You can see the probes in the following picture.
Even though the chips are rated with 125Kbps limitation, we manage to get stable communication at 500Kbps but only in one direction : CM5 to PC. In the picture below you can see the sequence of bytes sent from the CM5 to the Roboard and perfectly captured.
Pedro.
