Last Edit Ocober 10, 1996; July 9, 2001
Advantages of VLSI
If bipolar has been chosen over MOS because of speed, LSI is preferable
to SSI/MSI and VLSI is preferable to LSI for the same reasons.
First, costs are reduced with the larger devices. VLSI and LSI
require fewer parts and therfore fewer boards and therefore less
rack space. (One ASIC VLSI chip can replace a large, 14-layer fully
populated SSI/MSI board.) There is less external etch and fewer
pin connections as more of the interconnections are moved inside
Second, using LSI improves reliability. Approximately 80% of the
failures of working systems are caused by broken etch or bent pins
and other broken external connections. This is mechanical failure.
Using SSI/MSI a typical controller might use 300 16-pin DIPs, for
a total of 4800 pin connections. The same controller done with LSI
might use 30 40-pin DIPs, for a total of 1200 external pin connections,
the other interconnections having been moved to the inside of the
The AMD 2900 Family was used in this text. At the time it was published,
the 2900 Family was considered industry-standard for bipolar bit-slice
devices. It is a microprogrammable family of LSI-level complexity.
Table 1-2 summarizes its advantages.
Table 1-2 Microprogramming with LSI - Advantages over SSI/MSI
- More structured organization
- Field changes - may be as simple
as replacing a PROM
- Adaptations - may be as simple as
replacing a PROM
- Expansions - preplanned, may be as
simple as replacing or adding a PROM
- Better documentation
- Hardware and firmware can be designed
- LSI uses fewer parts
- LSI has better reliability
- Diagnostic PROM can aid debug, maintenance
The Am2900 Family
Note: Check out the AMD website - the 2900 family has a third-party
emulation available. The Am2900 Family itself is no longer in production.
I get e-mail.
As of 1981, the Am2900 family included
- CPU-ALU Am2910, Am2903, Am29203
- Microprogram sequencers and controllers Am2909/2911, Am2910
- Bipolar memory, error detection and correction controllers and
support devices, Am2960 series
- Interrupt controller Am2914, Am2913 and AM2902
- Bus I/O Am2950, etc.
- DMA support Am2940, Am2942
- Timing support via microprogrammable microcycles, Am2925
- Main memory program control, Am2930, Am2932
- 16-bit Am29116
Consider a simplex block diagram of a basic computer, shown in
Figure 1-1. The essential blocks of this diagram are:
- the CPU (central processing unit), containing the ALU and scratchpad
registers, the PC (program counter) and MAR (memory address register(s))
- the main memory (RAM) where active programs and data are stored
- peripherals, including back-up memory, input, output
- the CCU (central control unit), which supervises everything
else and contains the control logic instruction decode and the
Figure 1-1 Simplex system block diagram
The CPU is where data is processed; the CCU is where instructions
From this simple overview (a Von Neuman architecture) , progress
to Figure 1-2 and the generalized computer architecture blocked
out to show the various members of the 2900 Family and their applications.
Figure 1-2 Generalized computer architecture