ROM

Single Port Read Only Memory primitive.

MEMORY

Model

Pin	Function
`CS`	Chip Select (Active High). If Low, outputs are High-Z.
`RE`	Read Enable (Active High). If Low, outputs are High-Z.
`ADDR`	Address input bus.
`DATA`	Data output bus.

Operation

CS	RE	DATA
0	—	Z
1	0	Z
1	1	contents at ADDR

Initialization & Data Population

ROM contents are typically initialized using the DATA keyword within the PART statement. However, they can also be updated dynamically prior to simulation using the CLAMP command.

# Static initialization in netlist
PART=U1 TYPE=ROM DATA=X0, FF, AA, 55, 01

# Dynamic population in run script
CLAMP PART=U1 DATA=X100 01 02 03

For detailed information on the DATA syntax, X-handling behavior, and the CLAMP command, see the Memory Handling & Initialization guide.

X-Handling

If the Chip Select (CS) or Read Enable (RE) is X, the entire output data bus becomes X.
If any address bit is X, Simic identifies all possible addresses that match the bit-pattern. If the data at all matching addresses is identical, that value is output; otherwise, bits that differ are set to X.
If the number of X-bits in the address exceeds the global MAXX limit, the output is immediately forced to X for efficiency.

Physical Constraints

Address Depth: Supports up to 2^m+1 locations, where m+1 is the number of address pins.
Data Width: The data bus o=DATA[n:0] defines the word size (typically 1 to 64 bits).
Memory Limit: Large memories are handled efficiently using a sparse allocation technique, but very large address spaces may increase simulation startup time during DATA loading.

Equivalent Type Statement

Type=ROM i=CS,RE,ADDR[m:0] o=DATA[n:0]