Microcontrollers used in OEM systems

[Matt Sale]

> 
> Your point is well taken. Mind you, the P4 ECM PCB looks like it's 
> got plenty of room for more stuff...it's not dense at all :)

Depends on what you mean by dense :-) (pun intended).
> 
> 
> But seriously, the HC11 as it comes from Motorola can be had with an 
> 8-channel A/D converter and SCI built in. Why then does the P4 seem 
> to require a separate UART device and separate A/D converters?  If 
> cost minimalization was paramount, surely a few cheesy signal 
> conditioners (a few op amps, caps and resistors) would have been 
> cheaper than spreading block functionality (i.e. SCI, A/D etc) around 
> the board in separate chunks of silicon and the effort required to 
> route the PCB and place the parts...
> 
I'm a little rusty on which year each ECM was designed, so I'm
not even sure the P4 is an HC11.  And no, many of the earlier
systems don't use high-density PC boards, multi-layer
boards are expensive too.  Like you surmised, the cost tradeoff
analysis is extensive, and because technology changes so rapidly,
the best answer changes each year.  However, the auto companies
(not just GM) don't want to change their boxes every year, so
a box designed in 1985, introduced in 1988/9 (with 1985 technology)
could still be in production.  I'm exagerating a little, but not
much :-(.  

-- 
Matthew D. Sale,  IC Development Engineer, Delco Electronics Corp.
msale at iquest.net   http://www.iquest.net/~msale
'69 Mustang 351W 5-spd (13.464 at 103MPH using cave-man technology).

All responses are my own and should not be mistaken
for those of Delco Electronics or General Motors.