RAM
NAME_TABLE:
C_Function_Name: cm_d_ram
Spice_Model_Name: d_ram
Description: "digital random-access memory"
PORT_TABLE:
Port Name: data_in data_out
Description: "data input line(s)" "data output line(s)"
Direction: in out
Default_Type: d d
Allowed_Types: [d] [d]
Vector: yes yes
Vector_Bounds: [1 -] data_in
Null_Allowed: no no
PORT_TABLE:
Port Name: address write_en
Description: "address input line(s)" "write enable line"
Direction: in in
Default_Type: d d
Allowed_Types: [d] [d]
Vector: yes no
Vector_Bounds: [1 -] -
Null_Allowed: no no
PORT_TABLE:
Port Name: select
Description: "chip select line(s)"
Direction: in
Default_Type: d
Allowed_Types: [d]
Vector: yes
Vector_Bounds: [1 16]
Null_Allowed: no
PARAMETER_TABLE:
Parameter_Name: select_value
Description: "decimal active value for select line comparison"
Data_Type: int
Default_Value: 1
Limits: [0 32767]
Vector: no
Vector_Bounds: -
Null_Allowed: yes
PARAMETER_TABLE:
Parameter_Name: ic
Description: "initial bit state @ dc"
Data_Type: int
Default_Value: 2
Limits: [0 2]
Vector: no
Vector_Bounds: -
Null_Allowed: yes
PARAMETER_TABLE:
Parameter_Name: read_delay
Description: "read delay from address/select/write.en active"
Data_Type: real
Default_Value: 100.0e-9
Limits: [1.0e-12 -]
Vector: no
Vector_Bounds: -
Null_Allowed: yes
PARAMETER_TABLE:
Parameter_Name: data_load address_load
Description: "data_in load value (F)" "addr. load value (F)"
Data_Type: real real
Default_Value: 1.0e-12 1.0e-12
Limits: - -
Vector: no no
Vector_Bounds: - -
Null_Allowed: yes yes
PARAMETER_TABLE:
Parameter_Name: select_load
Description: "select load value (F)"
Data_Type: real
Default_Value: 1.0e-12
Limits: -
Vector: no
Vector_Bounds: -
Null_Allowed: yes
PARAMETER_TABLE:
Parameter_Name: enable_load
Description: "enable line load value (F)"
Data_Type: real
Default_Value: 1.0e-12
Limits: -
Vector: no
Vector_Bounds: -
Null_Allowed: yes
- Description:
The digital RAM is an M-wide, N-deep random access memory element with programmable select lines, tristated data out lines, and a single write/~read line. The width of the RAM words (M) is set through the use of the word width parameter. The depth of the RAM (N) is set by the number of address lines input to the device. The value of N is related to the number of address input lines (P) by the following equation: [2^{P} = N]There is no reset line into the device. However, an initial value for all bits may be specified by setting the ic parameter to either 0 or 1. In reading a word from the ram, the read delay value is invoked, and output will not appear until that delay has been satisfied. Separate rise and fall delays are not supported for this device.
Note that UNKNOWN inputs on the address lines are not allowed during a write. In the event that an address line does indeed go unknown during a write, the entire contents of the ram will be set to unknown. This is in contrast to the data in lines being set to unknown during a write; in that case, only the selected word will be corrupted, and this is corrected once the data lines settle back to a known value. Note that protection is added to the write en line such that extended UNKNOWN values on that line are interpreted as ZERO values. This is the equivalent of a read operation and will not corrupt the contents of the RAM. A similar mechanism exists for the select lines. If they are unknown, then it is assumed that the chip is not selected.
Detailed timing-checking routines are not provided in this model, other than for the enable delay and select delay restrictions on read operations. You are advised, therefore, to carefully check the timing into and out of the RAM for correct read and write cycle times, setup and hold times, etc. for the particular device they are attempting to model.
Example SPICE Usage:
a4 [3 4 5 6] [3 4 5 6] [12 13 14 15 16 17 18 19] 30 [22 23 24] ram2
.model ram2 d_ram(select_value = 2 ic = 2 read_delay = 80e-9)