Intel mcs-48 manual Keyboard, RD Display

EXPANDED MCS-48 SYSTEM

A high to low transition of the PROG line indi- cates that address is present while a low to high transition indicates the presence of data. Additional 8243'smay be added to the four bit bus and chip selected using additional output lines from the 8048/8748.

I/O Port Characteristics

Each of the four 4-bit ports of the 8243 can serve as either input or output and can pro- vide high drive capability in both the high and low state.

3.3.2I/O Expansion with Standard Peripherals

Standard MCS-80/85 type I/O devices may be added to the MCS-48 using the same bus and timing used for Data Memory expan- sion. I/O devices reside on the Data Memory bus and in the data memory address space and are accessed with the same MOVX instructions. See the previous section on data memory expansion for a description of timing. The following are a few of the Standard MCS-80 devices which are very useful in MCS-48 systems.

8214 Priority Interrupt Encoder

8251 Serial Communications Interface

8255 General Purpose Programmable I/O

8279 Keyboard/Display Interface

8253 Intervallimer

See Chapter 7 for detailed data sheets on these and other components.

3.3.3Combination Memory and I/O Expanders

As mentioned in the sections on program and data memory expansion the 8355/8755 and 8155 expanders also contain I/O capability.

8355/8755: These two parts are ROM and EPROM equivalents and therefore contain the same I/O structure. I/O consists of two 8-bit ports which normally reside in the exter- nal data memory address space and are ac- cessed with MOVX instructions. Associated with each port is an 8-bit Data Direction Reg- ister which defines each bit in the port as either an input or an output. The data direction registers are directly addressable thereby al- lowing the user to define under software con- trol each individual bit of the ports as either input or output. All outputs are statically latched and double buffered. Inputs are not latched.

8155/8156: I/O on the 8155/8156 isconfig- ured as two 8-bit programmable I/O ports and one 6-bit programmable port. These three registers and a Control/Status regis- ter are accessible as external data memory with the MOVX instructions. The contents of the control register determines the mode of the three ports. The ports can be programmed as input or output with or without associated handshake communi- cation lines. In the handshake mode, lines of the six,..bit port become input and out- put strobes for the two 8-bit ports. See the

		8	KEYBOARD
			INPUTS
INT	INT
P20	CfD
8048	8279		SCAN
	KEYBOARD		OUTPUTS
RD	RD DISPLAY		(A) DISPLAY
WR	WR
			OUTPUT
BUS			(B)DISPLAY
	CS		OUTPUT

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KEYBOARD/DISPLAY INTERFACE

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