Intel mcs-48 manual Expanded MCS-48 System, Expansion Examples See Also Chapter

EXPANDED MCS-48 SYSTEM

data sheet in Chapter 6 for details. Also included in the 8155 is a 14-bit program- mable timer. The clock input to the timer and the timer overflow output are available on external pins. The timer can be pro- grammed to stop on terminal count or to continuously reload itself. A square wave or pulse output on terminal count can also be specified.

1/0 Expansion Examples

(See Also Chapter 5)

The accompanying figure shows the expansion of 1/0 using multiple 8243'sThe. only difference from a single 8243 system is the addition of chip selects provided by additional 8048 OLitput lines. Two output lines and a decoder could also be used to address the four chips. Large numbers of 8243'swould require achip select decoder chip such as the 8205 to save 1/0 pins.

Also shown is the 8048 interface to a stan- dard MCS-80 peripheral; in this case, the 8255 Programmable Peripheral Interface, a 40 pin part which provides three 8-bit pro- grammable I/O ports. The 8255 bus interface is typical of programmable MCS-80 peripher- als with an 8-bit bidirectional data bus, a RD and WR input for Read/Write control, a CS

(chip select) input used to enable the Read/ Write control logic and the address inputs used to select various internal registers.

A.,

	A,	8255	PORT
	PROGRAMMABLE		A
8048 ALE		PERIPHERAL	PORT
		INTERFACE
Fi15			B
			PORT
			C
	OPTION #,
P20	Ao
P21	A,	8255	PORT
			A
	PROGRAMMABLE
		PERIPHERAL	PORT
8048		INTERFACE
AD	AD		B
ViR	FA		PORT
			C
BUS	00·7
		cs

-=-

OPTION #2

INTERFACE TO MCS-SO PERIPHERALS

PORT 1

8048

PROGI------~-----__+------~---______'

LOW COST 1/0 EXPANSION

3-8