MA2909 Datasheet | Gec Plessey

features include: I 4-bit cascadable microprogram counter. I 4 x 4 file with stack counter supporting nesting microsubroutines. I Zero input for returning to the zero microcode word. I Individual OR input for each bit for branching to higher microinstructions (2909 only). The 2909 is a 4-bit wide address controller intended for sequencing through a series of microinstructions contained in a ROM or PROM. Two 2909s may be interconnected to generate an 8-bit address (256 words), and three may be used to generate a 12-bit address (4K words). The 2909 can select an address from any of four sources: 1) A set of external direct inputs (D); 2) External data from the R inputs, stored in an internal register; 3) A four-word push/pop stack; or 4) A program counter register (which usually contains the last address plus one). The push/pop stack includes certain control lines so that it can efficiently execute nested subroutine linkages. Each of the four outputs can be OR’ed with an external input for conditional skip or branch instructions, and a separate line forces the outputs to all zeroes. The outputs are three-state. The 2911 is an identical circuit to the 2909 except the four OR inputs are removed and the D and R inputs are tied together. FEATURES I Fully patible with Industry Standard 2909A and 2911A ponents I Radiation Hard CMOS SOS Technology I High SEU Immunity I High Speed / Low Power I Fully TTL patible MA2909/11 STK PTR Figure 1: Microprogram Sequencer Block Diagram MA2909/11 The 2909/2911 are CMOS SOS microprogram sequencers intended for use in high-speed microprocessor applications. The device is a cascadable 4-bit slice such that two devices allow addressing of up to 256 words of microprogram and three devices allow addressing of up to 4K words of microprogram. A detailed logic diagram is shown in figure 1. The device contains a four input multiplexer that is used to select either the address register, direct inputs, microprogram counter, or file as...