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Bryan Pape · 10-05-2004, 06:46 PM

Quote: Originally Posted by dacndar

Hello everyone,
Here is what I see as the difficulty in using the XM direct to replace the XMPCR.
I got one over the weekend along with a smart adapter for Sony head units. I wanted to see if the XM direct could be used with software applications already written for the XMPCR. Last year, I built a stand-alone controller for my PCR with LCD display and IR remote control capability. It was getting close to completion but when the Roady 2 came out I figured why am I going through all this trouble to build it myself and I abandoned the project. So I know how to successfully talk to the XM tuner module that is in the PCR and I believe also in the XM direct.
The first problem is that even though the XMdirect uses the same "can" tuner module as the PCR and most other XM products, the data input from the smart adapter connected between your head unit and the XM direct, translates the protocol from whatever brand head unit you have to the protocol that the XM direct understands. In other words, the data input comming in on the mini 8 pin connector on the XM direct unit goes through an RS232 to TTL level converter (max3221) then to a microprocessor (an ATMEL mega8) in the XM direct unit and then to the XM "can" tuner module . A proprietary protocol is used between the head unit, the smart adapter and the XM direct unit. The smart adapter also has a microprocessor in it (ATMEL Mega32) which translates communications from the head unit to a protocol which the XM direct understands. In contrast, in the XMPCR, the data from your pc goes through a USB to serial converter chip (FTDI) in the XMPCR and then directly to TX and RX of the the "can" tuner module. So while it is not impossible to use the XMdirect as a PCR, it will require some modifications to bypass the CPU in the XM direct and talk directly to the tuner module. There is an RS232 to TTL converter chip in the XM direct (MAX3221). Which can be used to talk with the serial port of a PC but the ATMEL CPU must be bypassed or disabled. The ATmel CPU can be tri-stated by holding reset low. This would eliminate having to cut traces to isolate it from the tuner module. This would allow you to communicate with the XMdirect using a serial port and the existing software out there but if you want USB connection then another driver chip will be required. I'm wondering if it really is worth the trouble.

You mentioned that this is an Atmel. Is it an AVR? If so, what kind of package. (I'll have to look at the XMPCR to see what it's using) Perhaps it's possible to reprogram with JTAG (from a parallel port). Additionally, it seems to me that figuring out the "proprietary protocol" used between the headunit and the XM Direct should actually be rather straight forward - i.e. If you press a button, what does it spit out. The nice thing is that the 8-pin din is already RS-232 instead of TTL. I would think that creating an interface in software should actually be rather easym.

10-05-2004, 06:46 PM	#8
Bryan Pape Low Bitrate Join Date: Apr 2004 Posts: 74	Quote: Originally Posted by dacndar Hello everyone, Here is what I see as the difficulty in using the XM direct to replace the XMPCR. I got one over the weekend along with a smart adapter for Sony head units. I wanted to see if the XM direct could be used with software applications already written for the XMPCR. Last year, I built a stand-alone controller for my PCR with LCD display and IR remote control capability. It was getting close to completion but when the Roady 2 came out I figured why am I going through all this trouble to build it myself and I abandoned the project. So I know how to successfully talk to the XM tuner module that is in the PCR and I believe also in the XM direct. The first problem is that even though the XMdirect uses the same "can" tuner module as the PCR and most other XM products, the data input from the smart adapter connected between your head unit and the XM direct, translates the protocol from whatever brand head unit you have to the protocol that the XM direct understands. In other words, the data input comming in on the mini 8 pin connector on the XM direct unit goes through an RS232 to TTL level converter (max3221) then to a microprocessor (an ATMEL mega8) in the XM direct unit and then to the XM "can" tuner module . A proprietary protocol is used between the head unit, the smart adapter and the XM direct unit. The smart adapter also has a microprocessor in it (ATMEL Mega32) which translates communications from the head unit to a protocol which the XM direct understands. In contrast, in the XMPCR, the data from your pc goes through a USB to serial converter chip (FTDI) in the XMPCR and then directly to TX and RX of the the "can" tuner module. So while it is not impossible to use the XMdirect as a PCR, it will require some modifications to bypass the CPU in the XM direct and talk directly to the tuner module. There is an RS232 to TTL converter chip in the XM direct (MAX3221). Which can be used to talk with the serial port of a PC but the ATMEL CPU must be bypassed or disabled. The ATmel CPU can be tri-stated by holding reset low. This would eliminate having to cut traces to isolate it from the tuner module. This would allow you to communicate with the XMdirect using a serial port and the existing software out there but if you want USB connection then another driver chip will be required. I'm wondering if it really is worth the trouble. You mentioned that this is an Atmel. Is it an AVR? If so, what kind of package. (I'll have to look at the XMPCR to see what it's using) Perhaps it's possible to reprogram with JTAG (from a parallel port). Additionally, it seems to me that figuring out the "proprietary protocol" used between the headunit and the XM Direct should actually be rather straight forward - i.e. If you press a button, what does it spit out. The nice thing is that the 8-pin din is already RS-232 instead of TTL. I would think that creating an interface in software should actually be rather easym.