Hi Matt,

Get be happy! I found out the dream of the s/w (and h/w) developers. It is MSP430 microcontroller family of Texas Instruments. It is tremendous. It is that you wished.

1) The instruction set with seven addressing mode is like the very PDR-11! There is not the accumulator at all. The code needs 33% to 55% of the code lines compared to other microcontrollers.
For example:
;The MSP430 program sequence for the incrementing of a 16-bit counter
COUNT INC COUNTER ;Increment COUNTER

;The 8051 code for the incrementing of a 16-bit counter
COUNT: PUSH ACC ;Save Acc
INC COUNTER ;Increment COUNTER
MOV A,COUNTER ;Zero
JNZ EOCNT ;check
INC COUNTER+1 ;Store back the result
EOCNT: POP ACC ;Restore Acc

You can write your own operation system in 8 KB like RT11SJ for PDP-11!

2) The price is about 0.99$.

3) The chips of this family have 20 to 100 pins.

For instance, MSP430F149 has 60 KB flash, 2 KB RAM, 16-bit timer, 12-bit ADC, USART, UART/SPI, 8x8 to 16x16 HW multiplier, 48 i/o, 250 mA at 1 MHz 2.2 V, 64 pins (QFP).

Look at www.ti.com/msp430 or www.ti.com/sc/ampic. Besides, I have MSP430 family CD if you are interesting in details.

Good luck,
George