Section 1 ½ Microprogram-Based Processors 155
 

Table 2 Bit Slices
 

	Intel3002/3001	Am2901/2909	Am2903/2910	TI SN74S481/482	Motorola Mc 10800/10801
Technology	Schottky TTL	Schottky TTL	Schottky TTL	Schottky TTL	ECL
Number of pins per package:
Data part	28	40	48	48	48
Controller	40	28	40	20	48
Cycle time (m s)	0.1-0.2	0.1-0.2	0.1-0.2	0.1-0.14	0.01-0.05
Slice width (bits)	2	4	4	4	4
Maximum microstore size	512	Address expandable in 4-bit slices	4K	Address expandable in 4-bit slices	Address expandable in 4-bit slices
Register file size	11	16	16	external	external
Stack size	. . . . . . . . . . . ..	4	5	4 (in controller)	4
Basic instruction-set size	50	168	265	93	78
Year introduced	1975	1976	1977	1976	1977

 

Inevitably the answer will be, To speed up the emulation of a particular function found in another ISP. By studying these added features, the reader should develop an awareness of the level of complexity required in contemporary computer design. Table 3 summarizes the major differences between the 2901/2909 and 2903/2910 chip sets. Some points to observe are listed below.

• The 2901 comes in a 40-pin package, whereas the 2903 employs a 48-pin package. The extra pins are used for a second direct ALU input, increased ALU destination and functions, and chip programmability. In addition, some pins on the 2903 have time-multiplexed functions, thus increasing the functionality of the pins in common between the 2901 and 2903.

• The 2901 has a 9-bit microinstruction field: 3 bits for ALU source, 3 bits for ALU destination, and 3 bits for ALU function. The 2903 uses 9 bits plus 2 special bits for an 11-bit microinstruction field: 3 bits for ALU source, 4 bits for ALU destination, and 4 bits for ALU function (more extensive logic operations, arithmetic operations involving the carry bit, and 3-address microinstructions).

• Pins are set aside on the 2903 for chip position programmability. Whereas the 2901 deals primarily with boolean and 2's complement data-types, the position of the bit slice in a data word is immaterial. The added functions on the 2903 such as NORMALIZE and SIGNED MULTIPLY require that a bit slice be identified as a least significant, middle- significant, or most significant slice. The function per formed in a single operation may differ according to the slice's relative position. (Note that the 2901 can perform all the functions of the 2903 by utilizing more microcode and/or more external hardware. For example, the 2's complement multiplication in Chap. 13 takes five 2901 microinstructions, whereas only three microinstructions are required for the 2903 in Chap. 14.)

• There are additional functions on the 2903 to handle more extended data-types and operators. In particular, normalization (for floating-point mantissa operation), data- representation conversion between 2's complement and sign/magnitude (again for floating-point mantissa manipulation), unsigned/2's complement multiplication, 2's complement division, byte swapping, parity generation, and incrementation by 1 or 2 are functions more representative