Nuts & Volts - January 2006

S

T

A

M

P

A

P

L

I

C

A

T

I

O

N

S

and read the RC port. Just one caveat: the SX uses 0 to indicate an output bit, and 1 to indicate an input bit — this is exactly opposite of what we do in the BASIC Stamp (DIRS register). Knowing this, we will send BASIC Stamp style data to the PlayStation Helper module and invert the bits before assigning the configuration value to the TRIS register. Here’s the code for handling the extra I/O port:

Config_IoPort:
  char = RX_BYTE
  PlpIO = char
  char = ~char
  TrisIO = char
  GOTO Main

Write_IoPort:
  IoPort = RX_BYTE
  GOTO Main

Read_IoPort:
  WAIT_MS 1
  TX_OUT ~IoPort
  GOTO Main

One of the things that you’ll notice about the Config_IoPort section is that the SX pull-ups are activated on any pin that is made an input. Now this means that inputs will be active-low, so we’ll invert the bits sent back to the BASIC Stamp to make them look active-high — just as we did with the controller button bits.

WHAT ABOUT FORCE FEEDBACK?

To be honest, I was really hoping to conquer the force feedback motor control before using the SX with the PlayStation controller; sadly, every one of my attempts has failed. I have scoured the Internet for information and while there is some information out there, it is usually incomplete and not documented. What I’m going to be forced to do, I think, is rent or borrow a console and connect a logic analyzer to the PsxAttn, PsxClock, PsxCmd, and

■ FIGURE 4. PSX helper test output

PsxData lines to see exactly what happens when the motors are activated. Unfortunately, my friend Jim doesn’t have a multi-channel logic analyzer and couldn’t do that for me — and it’s not something that can be done with a two-channel scope; one needs to know what the console and controller are doing and in relation to each other.

I tell you what ... if you have a console and are able to do that analysis for me, I will send you a shiny new Parallax Professional Development Board. Here’s the offer: the first person that sends me working code, or enough information that I can add working code (that is, independent motor control through the seria link) to this project wins the PDB.