Intel mcs-48 manual 30AFN-00744A-14, Mode Definition Summary, Only

8'255A18255A·5

Mode Definition Summary

		MODE a	MODE'		MODE 2
	IN	OUT	IN	OUT	GROUPAONLV
PAo	IN	OUT	IN	OUT	..		~.
PB,	IN	OUT	IN	OUT	---
PAl	IN	OUT	IN	OUT	..
PA2	IN	OUT	IN	OUT			~
PA3	IN	OUT	IN	OUT	-
PA4	IN	OUT	IN	OUT
PAS	IN	OUT	IN	OUT
PAa	IN	OUT	IN	OUT				1
PA7	IN	OUT	IN	OUT
PBa	IN	OUT	IN	OUT	--
					--
PB2	IN	OUT	IN	OUT	--
PB3	IN	OUT	IN	OUT	--			J	MODE 0
PB4	IN	OUT	IN	OUT	--				OR MODE 1
PBS	IN	OUT	IN	OUT	--				ONLY
PBa	IN	OUT	IN	OUT	--
PB7	IN	OUT	IN	OUT		--
PCa	IN	OUT	INTRB	INTRB		I'D
PC,	IN	OUT	IBFB	OBFB		I/O
PC2	IN	OUT	STBB	ACKB		I/O
PC3	IN	OUT	INTRA	INTRA		INTRA
PC4	IN	OUT	rnA	I/O		STBA
PCs	IN	OUT	IBFA	I/O		IBFA
pca	IN	OUT	I/O	ACKA		ACKA
PC7	IN	OUT	I/O	OBFA		OBFA

Special Mode Combination Considerations

There are several combinations of modes when not all of the bits in Port C are used for control or status. The remaining bits can be used as follows:

If Programmed as Inputs -

All input lines can be accessed during a normal Port C read.

If Programmed as Outputs -

Bits in C upper (PC7-PC41 must be individually accessed using the bit set/reset function.

allows the programmer to test or verify the "status" of each peripheral device and change the program flow accordingly.

There is no special instruction to read the status informa- tion from Port C. A normal read operation of Port C is executed to perform th is fu nction.

INPUT CONFIGURATION

Bits in Clower (PC3-PCol can be accessed using the bit set/reset function or accessed as a threesome by writing into Port C.

Source Current Capability on Port B and Port C

Any set of eight output buffers, selected randomly from Ports Band C can source 1mA at 1.5 volts. This feature allows the "8255 to directly drive Darlington type drivers and high-voltage displays that require such source current.

Reading Port C Status

OUTPUT CONFIGURATION

i " j ,

GRQUPAGROUPS

Figura 1.5. MODE 1 Status Word Format

01 0 6 Os 04 03 D2 0, Do

IOBF. IINTE, IIBFA IINTE·IINTRAt><IXk><1

In Mode 0, Port C transfers data to or from the peripheral device. When the 8255 is programmed to function in Modes 1 or 2, Port C generates or accepts "hand-shaking" signals with the peripheral device. Reading the contents of Port C

,i"'

GROUP A GROUP 8

(DEFINED BY MODe 0 OR MODE 1 SELECTION)

Figura 18. MODE 2 Statu. Word Format

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