Read Only Memory DC A0A0 A b1b1 b2b2 Programmable ROM DC A0A0 A v b1b1 b2b Fuse Mask-programmed ROM

DC A0A v b1b1 b2b tension 2U 1 tension U 1 tension 0 The only fuse that falls under the voltage of 2U resulting in its melting Programming of EPROM A1A1

n pp Silicon floating gate Silicon select gate V ss V dd V gg EPROM array V dd WL i Wl i+1 BL i Bl i+1 00 EPROM, EEPROM and Flash

Combinational Circuits Boolean function x 1 x 2 x n y y = f (x 1,x 2,… x n ) Knowing the logical values of inputs at a certain moment of time enables us to calculate the value of the output by using the Boolean function. Dependence on the values of previous inputs does not exist. Sequential Circuits Boolean function + state x 1 x 2 x n y In order to determine the value of the output at a certain moment of time it is necessary to know both the values of the inputs at a certain moment of time as well as state that is dependent on the values of the previous inputs. Clock input t determines when transition from one state to another takes place. t Output function Transition function Memory x 1 x n y1y1 Old state t New state amam asas Use of ROM in realising the hardware ymym... Realisation of combinational circuits in ROM.

Address X4X4 X3X3 X2X2 X1X ROM Example: Running of a segment indicator by ROM.

Combinational circuit InputsOutputs Memory Old state New state t (clk) Realisation of a synchronous sequential circuit on ROM

ROM InputsOutputs Direct Feedback ROM Inputs Outputs Registered Feedback Register t (clk) Feedback

ROM a0a0 a1a1 a2a2 a3a3 a4a4 clk o1o1 o2o2 o3o3 o4o4 etc... Example. 4-bit synchronous counter

ROM a0a0 a1a1 a2a2 clk o0o0 o1o1 o2o2 o3o3 x1x1 z1z1 z2z2 y1y1 y2y2 ab c / y 1 y 2 x 1 / y 1 y 2 - / y 1 y 2 x 1 / y 1 y 2 Beginning y 1 y 2 a b c x1x1 a End c Realisation of a synchronous automaton on ROM buffered with register

a b c - o0o0 o1o1 o2o2 o3o3 z 2 z 1 x 1 ROM table of an automaton

S0S0 S3S3 S2S2 S1S1 x 1 x 2 /v 1 x 1 x 2 /v 6 x 1 x 2 /v 7 x 1 x 2 /v 12 x 1 x 2 /v 3 x 1 x 2 /v 4 x 1 x 2 /v 9 x 1 x 2 /v 10 x 1 x 2 /v 2 x 1 x 2 /v 5 x 1 x 2 /v 7 x 1 x 2 /v Example ROM a0a0 a1a1 a2a2 a3a3 x1x1 o1o1 o2o2 o3o3 x2x2 onon Outputs State Realisation of an asynchronous automaton on ROM

Inputs State`State Outputs of the automaton ROM address inputs ROM data outputs ROM table

y 1 = x 3 x 2 x 1 + x 3 x 2 x 1 + x 3 x 2 = x 3 x 2 x 1 + x 3 x 2 x 1 + x 3 x 2 x 1 + x 3 x 2 x 1 y 2 = x 3 x 2 x 1 + x 3 x 2 = x 3 x 2 x 1 + x 3 x 2 x 1 + x 3 x 2 x 1 DC x1x1 a0a0 x2x2 a1a1 x3x3 a3a y1y1 y2y2 Decoder realises all possible conjunctions from all input variables. In case of the following example four different conjunctions should be realised. Decoder as a realiser of conjunctions

&1 1 1 A B C & & & & & & & Decoder realises all possible conjunctions from all input variables Decoder

111 +V y1y1 y2y2 y m x 1 x 2 x n + V Buffer ANDOR x 1 x 2 x n y1y1 y2y2 y m Programmable arrays. PLA - Programmable Logic Array, PAL - Programmable Array Logic

1 +V... +V y1y1 y2y2 y m x 1 x 2 x n Buffer NOR x 1 x 2 x n y1y1 y2y2 y m V 0 0 NOR – NOR array

Buffer AND – fixed (decoder) OR – programmable y1y1 y2y2 y m Buffer AND – programmable OR – programmable x 1 x 2 x n y1y1 y2y2 y m Buffer AND – programmable OR – fixed x 1 x 2 x n y1y1 y2y2 y m ROM – Read Only Memory PLA – Programmable Logic Array PAL – Programmmable Array Logic Comparison of ROM,PAL and PLA

111 +V x 3x 3 x 2 x 1x 1 0 y 1 y 2 Example. y 1 = x 3 x 2 x 1 + x 3 x 2 x 1 + x 2 x 1 y 2 = x 3 x 2 x 1 + x 2 x 1 Realisation of a combination circuit on a PLA/PAL type of array.

PLA/PAL Memory x 1 x n y1y1 Old state t New state amam asas ymym... Output function transition function Output function Transition function Memory x 1 x n y1y1 Old state t New state amam asas ymym... Realisation of a sequential circuit on a PAL/PLA type of array.