Atari SIO: What is $4F device ID

[LessNick]

Hello everyone o/

 

I began to study the work of Atari SIO and ran into an interesting question.

 

I connected the Arduino to the Atari SIO pins and started listening to the broadcast that Atari asks for when it is turned on.

 

The first 28 packages were standard:
 

Received data: $31, $53, $0, $0, $84
CRC: Calculated: $84,  Received: $84,  Status:OK
Device: $31 ("1")
Command: $53 ("Get Status")

 

Atari tries to interrogate the first device ($ 31 = D1:) and requests its status.

 

Having exhausted all attempts, my atari requested an unknown device ($ 4F) and tried to send an unknown command ($ 40):

 

Received data: $4F, $40, $0, $0, $8F
CRC: Calculated: $8F,  Received: $8F,  Status:OK
Device: $4F ("O")
Command: $40 ("Unknown")

 

I found a description of the commands and device IDs on the site atarimax, but there is no $4F device among them and the $40 command is also not known.

Google search also failed.

 

Perhaps this is no secret to anyone and the information is available.

 

But I managed to find only the mention of the device ("O") in the RespeQt program.

 

Someone can tell where to find out a little more information.

 

Thank you in advance!

 

[LessNick]

Oh, just ask and the answer was found.

 

If I understand correctly, then $4F is not a device, but a bus poll.

 

 

And if I correctly understood the description on the site atariki, then something like this (1090) could be connected to the bus.

 

 

[+DrVenkman]

Search the site for the Altirra Hardware Reference Manual - it’s @phaeron’s ever evolving and updating creation that extensively documents the behavior of A8 hardware to support his efforts to refine the Altirra emulator. 

[flashjazzcat]

Search Google: it's the first hit:

 

http://www.virtualdub.org/downloads/Altirra Hardware Reference Manual.pdf

 

$4F is 'New Poll' or something like that.

[+Nezgar]

I believe this command was introduced in the 1200XL OS to allow polling devices and loading their handlers without having to overload D1: like the 850 does (responding on the 49th attempt to find a drive or something), which also prevents it from automatically loading it's handler if there actually is a D1:. This is documented in a 1200XL, maybe sweet 16 specification document somewhere, ill see if I can find it.

[+Nezgar]

Found it, in the section titled "5.0 Enhancements to the A400/800 Rev.B Operating System Incorporated in the A1200"

https://archive.org/details/AtariA1200OperatingSystemManualSupplement/page/n21

 

A400/800 OS: Type 0,1,2 device polls

 

"A1200 Handler Load and Relocation during Power-up Processing" - "OS Type 3 Poll" (Are you there?) - consists of type A "poll reset" and type B "Null poll"

 

"A1200 Application-Initiated Load" - "Type 4 Poll"

 

Both use Device Address $4F

[LessNick]

Thanks so much for the answers. I will study the proposed documentation.