Hello my friends, I hope you are well
I propose thus to EPROM convert a 16-bit to 8 bit
Currently the configuration is for a LOW-ROM (Mode 20):The A15 pin is in NC
This leaves the rom located in 00:8000 to 7D:FFFF and this make a mirror from 80:8000 to FF:FFFF
you can use the maximum size of 32 Mb, but from 7E to 7F it is reserved for the system (not available), which one, to use this memory loss, we must recover from the spaces of the mirror, FE: 8000 to FF:FFFF
through IC "SN74CB3Q3345" and A0 pin , we block or enable the passage of data (D0 - D7)
when A0 has a value of 0 (LOW), it C1 enable, and it C2 disable
when A0 has a value of 1 (HIGH), it C1 disable, and it C2 enable
this allows us to deliver the first 8 bit, then, submit the following 8 bit, of the 16 bit eprom
We can check this in this table
8 bit address = 1010
16 bit address = 101
convert 16 bit to 8 bit, taking away the last digit
then the first bit of address we can use to enable the first 8 bit, then the next 8 bit
I have only one question about my scheme, Pin 11 of C3 (EPROM) must be connected to / RD or / CS ?
regards
- : - : - : - : - UPDATE - : - : - : - : -
this CI -> SN74CB3Q3345 replace to SN74CBT16244C
Because, this work with 5V....
not forget that for every CI (integrated circuit) must be added capacitor
I propose thus to EPROM convert a 16-bit to 8 bit
Currently the configuration is for a LOW-ROM (Mode 20):The A15 pin is in NC
This leaves the rom located in 00:8000 to 7D:FFFF and this make a mirror from 80:8000 to FF:FFFF
you can use the maximum size of 32 Mb, but from 7E to 7F it is reserved for the system (not available), which one, to use this memory loss, we must recover from the spaces of the mirror, FE: 8000 to FF:FFFF
through IC "SN74CB3Q3345" and A0 pin , we block or enable the passage of data (D0 - D7)
when A0 has a value of 0 (LOW), it C1 enable, and it C2 disable
when A0 has a value of 1 (HIGH), it C1 disable, and it C2 enable
this allows us to deliver the first 8 bit, then, submit the following 8 bit, of the 16 bit eprom
We can check this in this table
8 bit address = 1010
16 bit address = 101
convert 16 bit to 8 bit, taking away the last digit
then the first bit of address we can use to enable the first 8 bit, then the next 8 bit
I have only one question about my scheme, Pin 11 of C3 (EPROM) must be connected to / RD or / CS ?
regards
- : - : - : - : - UPDATE - : - : - : - : -
this CI -> SN74CB3Q3345 replace to SN74CBT16244C
Because, this work with 5V....
not forget that for every CI (integrated circuit) must be added capacitor