*If interrupts are not authorized, then the R52 counter continues to increment and the interrupt remains armed (the Gate Array then maintains its INT signal). When interrupts are enabled (using the EI instruction) and '''after the instruction that follows EI''' (so not immediately after EI), bit5 of R52 is cleared and the interrupt takes place
Note: On Amstrad Plus, the Gate Array is not the sole generator of interrupts. The 3 DMA sound channels are each able to trigger an interrupt. The ASIC also provides an interrupt vector register (IVR) for vectorized interrupts. And it offers a programmable raster interrupt register (PRI) that can be used instead of the normal raster interrupt mechanism. And it provides an interrupt vector register (IVR) for vectorized interrupts.
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== Registers ==
Note: The Plus palette capabilities are only accessible through the [[Default I/O Port Summary|ASIC I/O page]]. Registers PENR and INKR are not needed in that case.
=== Register PENR (Select a color register) ===
=== Register RMR (Control Interrupt counter, ROM mapping and Graphics mode) ===
This is a general purpose register responsible for the [[Video modes|screen graphics mode]] and the ROM configuration.
==== Graphics mode selection ====
| 3 || x
|-
| 2 || x || rowspan="3" | Physical lower ROM number (0..7)
|-
| 1 || x
|}
The lower ROM address and [[Default I/O Port Summary|ASIC I/O page ]] modes are:
-Mode- ROM address ASIC I/O Page
11 &0000-&3FFF &4000-&7fff
The physical lower ROMs are also accessible as upper ROMs by using the [[Upper ROM Bank Number]] port and the RMR register.
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|-
| ''Hardware Number||Firmware Number|| ''Colour Name''
| ''R %'' || ''G %'' || ''B %'' || ''PlusASIC'' || ''Colour''
|-
| 0 (40h) || 13 || White || 50|| 50|| 50|| #666|| bgcolor="#808080" |
|-
| ''Firmware Number'' || ''Hardware Number'' || ''Colour Name''
| ''R %'' || ''G %'' || ''B %'' || ''PlusASIC'' || ''Colour''
|-
| 0|| 54h ||Black || 0|| 0|| 0|| #000||bgcolor="#000000"|
|18|| 52h ||Bright Green || 0||100|| 0|| #0F0||bgcolor="#00ff00"|
|-
|19|| 42h (or 51h) ||Sea Green || 0||100|| 50|| #0F00F6||bgcolor="#00ff80"|
|-
|20|| 53h ||Bright Cyan || 0||100||100|| #0FF||bgcolor="#00ffff"|
* [[CPC Palette]] - some more details
On the Plus, the Amstrad engineers converted the values of the R, G, and B subcomponents to the new 12-bit palette using this 4-bit scale:
* 0% became #0