Intel mcs-48 manual Combinations of Mode, Bidirectional Bus 1/0 Control Signal Definition

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Combinations of MODE 1

Port A and Port B can be individually defined as input or output in Mode 1 to support a wide variety of strobed I/O applications.

PA7,PAn

	PC,	STBA
	PC,	IBFA
	PC,	INTRA
	Pe 6. 7 -+2--I/O				I/O
	pe PDO	8
	"
	PC,
	pe2 -ACKB			PC,
		INTRB		PC.	INTRa
PORT A -	(STROBED INPUT)		PORT A -	(STROBED OUTPUT)
PORT B -	(STROBED OUTPUT)		PORT B -	(STROBED INPUT)

Figure 10. Combinations 01 MODE 1

Operating Modes

MODE 2 (Strobed Bidirectional Bus 1/0). This functional configuration provides a means for communicating with a peripheral device or structure on a single S·bitbus for both transmitting and receiving data (bidirectional bus 1/0). "Handshaking" signals are provided to maintain proper bus flow discipline in a similar manner to MODE

1.Interrupt generation and enableldisable functions are also available.

MODE 2 Basic Functional Definitions:

•Used in Group A only.

•One S-bit, bi-directional bus Port (Port A) and a 5-bit control Port (Port C).

•Both inputs and outputs are latched.

•The 5-bit control port (Port C) is used for control and status for the B-bit, bi-directional bus port (Port A).

Bidirectional Bus 1/0 Control Signal Definition

INTR (Interrupt Request). A high on this output can be used to Interrupt the CPU for both input or output opera- tions.

Output Operations

OBF (Output Buffer Ful). The OBF output will go "low" to indicate that the CPU has written data out to port A.

ACK (Acknowledge). A "low" on this input enables the tri-state output buffer of port A to send out the data. Otherwise, the output buffer will be In the high im- pedance state.

INTE 1 (The INTE Flip-Flop Associated with OBF)_ Con- trolled by bit setlreset of PCs.

Input Operations

STB (Strobe Input)

STB (Strobe Input)_ A "low" on this input loads data into the Input latch.

IBF (Input Buffer Full F/F)_ A "high" on this output in- dicates that data has been loaded into the input latch.

INTE 2 (The INTE Flip-Flop Associated with IBF)_ Con- trolled by bit setlreset of PC4•

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