MA780 Multiport Memory Option

The MA780 Multiport Memory Option was a MOS DRAM multi-port memory main memory system for the VAX-11/780; it allowed creation of multi-processor systems such as the VAX-11/782. It was 64 bits wide, to interface to the -11/780's Synchronous Backplane Interconnect (SBI), and provided ECC (8 bits/double-word), which could correct all single-bit errors.

Huge system made up of four VAX-11/780's connected to an MA780 Multiport Memory

An MA780 system was comprised of:

• the main MA780 unit, which contained a custom backplane holding i) a small group of control cards, and ii) a variable number of array cards (between 1 and 8 per MA780), holding the DRAM chips; and
• in each connected CPU (between 2 and 4), an MA780-C Port Interface, held in another, smaller custom backplane, which connected the main MA780 unit (up to two different ones per MA780-C) to the host CPU's SBI.

With the 256-Kbyte M8210 array card (shared with the MS780-C), this allowed a maximum of 2MB per MA780. The -11/780 thus supported up to 2 MA780 subsystems, for a maximum of 4MB with fully populated MA780's.

Implementation

The main MA780 was implemented on super hex cards, mounted in a custom 20-slot backplane. The cards were:

Slot	Board	Acronym	Function
1	M8210	MAY	Memory Array (optional)
...
8	M8210	MAP	Memory Array
9	M8210	MAP	Selective Map Cache (optional)
10	M8261	MPS	Multiport Port Synchronizer
11	M8212	MDT	Memory Data Paths
12	M8260	MAT	Multiport Array Timing
13	M8259	MPC	Multiport Port Control (Port 3 - optional)
14	M9045		BDI Connect (rear)
15	M8259	MPC	Multiport Port Control (Port 2 - optional)
16	M9045		BDI Connect (rear)
17	M8259	MPC	Multiport Port Control (Port 1)
18	M9045		BDI Connect (rear)
19	M8259	MPC	Multiport Port Control (Port 0)
20	M9045		BDI Connect (rear)

Slots 1-8 held 256-Kbyte M8210 array cards; a minimum of one, in slot 8, was required.

The MA780-C was mounted in a custom 20-slot backplane. The contents were:

Slot	Board	Acronym	Function
1			Blank
2	M9040/M8258		SBI Terminator / Multiport Port Interface (optional)
3	M8258		Multiport Port Interface
4	M9045		BDI Connect (rear)

External links

• VAX Maintenance Handbook VAX-11/780 1983 Edition (EK-VAXV2-HB-002) - the MA780 is covered on pp. 235-253
• VAX-11/780 Installation Manual (EK-SI780-IN-002) - the MA780 is covered in Chapter 9