Intel 8080 manual Applications of 8216/8226, Memory and 1/0 Interface to a Bi-directional Bus

SCHOTTKY BIPOLAR 8216/8226

APPLICATIONS OF 8216/8226 .

8080 Data Bus Buffer

The 8080 CPU Data Bus is capable of driving a single TTL load and is more than adequate for small, single board sys- tems. When expand ing such a system to more than one board to increase I/O or Memory size, it is necessary to provide a buffer. The 8216/8226 is a device that is exactly fitted to this application.

Shown in Figure 2 are a pair of 8216/8226 connected di- rectly to the 8080 Data Bus and associated control signals. The buffer is bi-directional in nature and serves to isolate the CPU data bus.

On the system side, the DB lines interface with standard semiconductor I/O and Memory components and are com- pletely TTL compatible. The DB lines also provide a high drive capability (50mA) so that an extremely large system can be dirven along with possible bus termination networks.

On the 8080 side the 01 and DO lines are tied together and are directly connected to the 8080 Data Bus for bi-directional operation. The DO outputs of the 8216/8226 have a high voltage output capability of 3.65 volts which allows direct connection to the 8080 whose minimum input voltage is

3.3volts. It also gives a very adequate noise margin of 350mV (worst case).

The DIEN inputs to 8216/8226 is connected directly to the 8080. OlEN is tied to DBIN so that proper bus flow is maintained, and CS is tied to BUSEN so that the system side Data Bus will be 3-stated when a Hold request has been acknowledged during a DMA activity.

The 8216/8226 can be used in a wide variety of other buf- fering functions in microcomputer systems such as Address Bus Drivers, Drivers to peripheral devices such as printers, and as Drivers for long length cables to other peripherals or systems.

			15
	4	01	OlEN	3
0 0	2	DO	DB	OBo
	7			6
0 1
	5		8216	OB1
	9
			8226	10
D2	11			OB2
	12			13
0 3
	14		cs	DB3

	SYSTEM
8080	OATA
	BUS
	15

	01	OlEN	3
D4		OB
	DO		OB4
			6

OsDBs

	8216
0 6	8226	10
		OB6
0 7		13
		DB7

CS

Memory and 1/0 Interface to a Bi-directional Bus

In large microcomputer systems it is often necessary to pro-

Figure 2. 8080 Data Bus Buffer.

vide Memory and I/O with their own buffers and at the same time maintain a direct, common interface to a bi-directional Data Bus. The 8216/8226 has separated data in and data out lines on one side and a common bi-directional set on the other to accomodate such a function.

Shown in Figure 3 is an example of how the 8216/8226 is used in this type of application.

The interface to Memory is simple and direct. The memories used are typically Intel® 8102, 81 02A, 8101 or 8107B-4 and have separate data inputs and outputs. The DI and DO lines of the 8216/8226 tie to them directly and under control of the MEMR signal, which is connected to the DIEN input, an interface to the bi-directional Data Bus is maintained.

The interface to I/O is similar to Memory. The I/O devices used are typically Intel® 8255s, and can be used for both input and output ports. The I/O R signal is connected di- rectly to the DI EN input so that proper data flow from the I/O device to the Data Bus is maintained.

MEMORYI/O

01	DO	01	DO
OlEN	(2) CS	OlEN	(2) CS
8216	(2)	8216	(2)
8226		8226

BUSEN ........----~

Figure 3. Memory and I/O Interface to a Bi-Directional Bus.

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