Action
Instruct the compiler to set options for external memory access.
Syntax
CONFIG XRAM = mode [ , WaitstateLS=wls , WaitStateHS=whs ]
Remarks
Mode |
The memory mode. This is either enabled or disabled. By default, external memory access is disabled. |
Wls |
When external memory access is enabled, some chips allow you to set a wait state. The number of modes depend on the chip. A modern chip such as the Mega8515 has 4 modes : 0 - no wait states 1 - 1 cycle wait state during read/write 2 - 2 cycle wait state during read/write 3 - 2 cycle wait state during read/write and 1 before new address output
WLS works on the lower sector. Provided that the chip supports this. |
Whs |
When external memory access is enabled, some chips allow you to set a wait state. The number of modes depend on the chip. A modern chip such as the Mega8515 has 4 modes : 0 - no wait states 1 - 1 cycle wait state during read/write 2 - 2 cycle wait state during read/write 3 - 2 cycle wait state during read/write and 1 before new address output
WHS works on the high sector. Provided that the chip supports this. |
Wait states are needed in case you connect equipment to the bus, that is relatively slow. Especial older electronics/chips.
Some AVR chips also allow you to divide the memory map into sections. By default the total XRAM memory address is selected when you set a wait state.
The $XA directive should not be used anymore. It is the same as CONFIG XRAM=Enabled.
When using IDLE or another power down mode, it might be needed to use CONFIG XRAM again, after the chip wakes from the power down mode.
See also
ASM
NONE
Example
CONFIG XRAM = Enabled, WaitstateLS=1 , WaitstateHS=2