Hades logoHades applet banner
Intel MCS4 I/O ports

applet icon

The image above shows a thumbnail of the interactive Java applet embedded into this page. Unfortunately, your browser is not Java-aware or Java is disabled in the browser preferences. To start the applet, please enable Java and reload this page. (You might have to restart the browser.)

Circuit Description

This demonstration shows how to use the output ports of the 4002 integrated circuits to control external circuitry. To visualize the logic values on the output ports, a few LED components are connected to them.

The software running on the i4004 microprocessor consists of a simple endless loop that writes the bit-patterns 1000, 0100, 0010, 0001 to the first ROM chip, and then to the next ROM chip via the WRR instruction. In between, a little bookkeeping is necessary. To demonstrate this better, the circuit uses a very slow clock period (0.05 seconds).

; lauflicht.asm 
;
; MCS4 (i4004) program to demonstrate accessing the i4001 ROM chip ports.
; The circuit uses one i4004 CPU and two i4002 ROM chips.
;
; (C) 2003, 2004, 2005 by
; Andreas Ruge and Norman Hendrich
; Univ. of Hamburg, Dept. CS
;

START
	FIM R0R1, 0x24	; R0=2, R1=4
	FIM R2R3, 0x00	; R2=0, R3=0

	SRC R2R3	; select ROM chip #0
	LDM 8		; load value 8 (1000)
	WRR		; and write to ROM output
	LDM 4		;
	WRR		; write value 4 (0100) to ROM output
	LDM 2		;
	WRR		; write value 2 (0010) to ROM output
	LDM 1		;
	WRR		; write value 1 (0001) to ROM output
	LDM 0		;
	WRR		; write value 0 (0000) to ROM output

	CLB		; code to select ROM chip #1
	IAC		;
	XCH R2		;
	SRC R2R3	; 

	LDM 8		; load value 8 (1000)
	WRR		; and write to ROM output
	LDM 4		;
	WRR		; write value 4 (0100) to ROM output
	LDM 2		;
	WRR		; write value 2 (0010) to ROM output
	LDM 1		;
	WRR		; write value 1 (0001) to ROM output
	LDM 0		;
	WRR		; write value 0 (0000) to ROM output

	JUN START	; jump back (endless loop)

The following screenshot shows example waveforms produced during the simulation:

simulation waveforms

See also:

Print version | Run this demo in the Hades editor (via Java WebStart)
Usage | FAQ | About | License | Feedback | Tutorial (PDF) | Referenzkarte (PDF, in German)
Impressum http://tams-www.informatik.uni-hamburg.de/applets/hades/webdemos/80-mcs4/zaehler/lauflicht.html