XSCHEM Process agnostic Digital standard cell symbols.
Warning: This is currently Work in progress.
This directory contains symbols to be used in the XSCHEM schematic editor. For a quick XSCHEM introduction see this presentation.
These symbols represent a tentative list of digital logic standard cells to be used to build digital circuit schematics in XSCHEM.
The list is based on this document by Tim Edwards.
The symbols have simple names to make their function clear. In order to correctly bind to the Skywater PDK some additional work is needed. This is all work in progress.
GOAL
Provide a set of digital logic gates that can be used with xschem and seamlessly simulated using the Skywater 130 PDK as well as other foundry provided gate libraries and SPICE dimulation models. Allowing verilog simulation directly from Xschem is another goal.
SYMBOL DRAWINGS
CURRENT STATUS
The gates can be placed in a XSCHEM schematic and a valid spice netlist is generated for them. However in order to use the SKY130 PDK circuit description some wrapper must be provided. In their final implementation, these gates will bind directly to the Skywater 130 PDK models. Currently the cells have 4 attributes to set supply and ground net names for source and body connections:
GATE FUNCTION DESCRIPTION
#----------------------------------------------------------------------- # List of standard gate symbols with mapping to liberty file fields # # Y, X refer to logic output pins # C, S, ... refer specifically to adder carry and sum output pins # Q, QB refer specifically to flip-flop or latch output pins # IQ, IQB refers to function entries for flops. "I" is literal. # A, B, C, ... refer to input pins # D, R, S, ... refer specifically to flip-flop input pins # SD refers to scan data input pin for flip-flops # CI refers specifically to full adder carry-in input # Z refers to high-impedance state # & means AND # | means OR # ! means NOT # ( ) groups # # Symbol Liberty Liberty # primitive file field # name field value ... #----------------------------------------------------------------------- AND2 function Y=A&B AND3 function Y=A&B&C AND4 function Y=A&B&C&D AND5 function Y=A&B&C&D&E AND8 function Y=A&B&C&D&E&F&G&H AND2I function Y=!A&B AO21 function Y=(A&B)|C AO22 function Y=(A&B)|(C&D) AOI21 function Y=!((A&B)|C) AOI22 function Y=!((A&B)|(C&D)) NAND2 function Y=!(A&B) NAND3 function Y=!(A&B&C) NAND4 function Y=!(A&B&C&D) NAND5 function Y=!(A&B&C&D&E) NAND8 function Y=!(A&B&C&D&E&F&G&H) NAND2I function Y=!(!A&B) OR2 function Y=A|B OR3 function Y=A|B|C OR4 function Y=A|B|C|D OR5 function Y=A|B|C|D|E OR8 function Y=A|B|C|D|E|F|G|H OR2I function Y=!A|B OA21 function Y=(A|B)&C OA22 function Y=(A|B)&(C|D) OAI21 function Y=!((A|B)&C) OAI22 function Y=!((A|B)&(C|D)) NOR2 function Y=!(A|B) NOR3 function Y=!(A|B|C) NOR4 function Y=!(A|B|C|D) NOR5 function Y=!(A|B|C|D|E) NOR8 function Y=!(A|B|C|D|E|F|G|H) NOR2I function Y=!(!A|B) XOR2 function Y=(A&!B)|(!A&B) XNOR2 function Y=(A&B)|(!A&!B) INV function Y=!A BUF function Y=A TBUF function Y=A three_state E TBUFI function Y=A three_state !E MUX2 function Y=(A&C)|(B&!C) MUX2I function Y=!((A&!C)|(B&C)) MUX4 function Y=(A&!E&!F)|(B&!E&F)|(C&E&!F)|(D&E&F) MUX4I function Y=!((A&!E&!F)|(B&!E&F)|(C&E&!F)|(D&E&F)) HA function C=A&B function S=(A&!B)|(!A&B) FA function C=(A&B)|(A&CI)|(B&CI) function S=(A&B&CI)|(!A&B&!CI)|(!A&!B&CI)|(A&!B&!CI) LATCH function Q=IQ enable E data_in D LATCHI function Q=IQ enable !E data_in D LATCHR function Q=IQ enable E data_in D clear !R LATCHIR function Q=IQ enable !E data_in D clear !R LATCHSR function Q=IQ enable E data_in D preset !S clear !R LATCHISR function Q=IQ enable E data_in D preset !S clear !R LATCHQ function Q=IQ QB=IQB enable E data_in D LATCHIQ function Q=IQ QB=IQB enable !E data_in D LATCHRQ function Q=IQ QB=IQB enable E data_in D clear !R LATCHIRQ function Q=IQ QB=IQB enable !E data_in D clear !R LATCHSRQ function Q=IQ QB=IQB enable E data_in D preset !S clear !R LATCHISRQ function Q=IQ QB=IQB enable !E data_in D preset !S clear !R DFF function Q=IQ clocked_on C next_state D DFFQ function Q=IQ function QB=IQB clocked_on C next_state D DFFS function Q=IQ clocked_on C next_state D preset !S DFFR function Q=IQ clocked_on C next_state D clear !R DFFSR function Q=IQ clocked_on C next_state D preset !S clear !R DFFSQ function Q=IQ function QB=IQB clocked_on C next_state D preset !S DFFRQ function Q=IQ function QB=IQB clocked_on C next_state D clear !R DFFSRQ function Q=IQ function QB=IQB clocked_on C next_state D clear !R preset !S DFFI function Q=IQ clocked_on !C next_state D DFFIQ function Q=IQ function QB=IQB clocked_on !C next_state D DFFIS function Q=IQ clocked_on !C next_state D preset !S DFFIR function Q=IQ clocked_on !C next_state D clear !R DFFISR function Q=IQ clocked_on !C next_state D preset !S clear !R DFFISQ function Q=IQ function QB=IQB clocked_on !C next_state D preset !S DFFIRQ function Q=IQ function QB=IQB clocked_on !C next_state D clear !R DFFISRQ function Q=IQ function QB=IQB clocked_on !C next_state D clear !R preset !S EDFF function Q=IQ clocked_on C next_state (D&E)|(IQ&!E) EDFFQ function Q=IQ QB=IQB clocked_on C next_state (D&E)|(IQ&!E) SDFF function Q=IQ clocked_on C next_state (D&!E)|(SD&E) SDFFQ function Q=IQ QB=IQB clocked_on C next_state (D&!E)|(SD&E)