| 1 || 0 || 0 || style="text-align: center;" | n || All || RMR || Control Interrupt counter, ROM mapping and Graphics mode || Gate Array
|-
| rowspan="2"| 1 || rowspan="2"| 0 || rowspan="2"| 1 || style="text-align: center;" rowspan="2" | n || All || RMR || ''Ghost register'' || Gate Array (CPC) or locked ASIC (Plus)
|-
| 1 || 0 || 1 || style="text-align: center;" | n || Plus || RMR2 || ASIC & Advanced ROM mapping || Unlocked ASIC
|-
| 1 || 1 ||colspan=2 style="text-align: center;" | n || All || MMR || RAM memory mapping || PAL (only with 128KB or RAM expansion)
==== ROM configuration selection ====
Bit 2 is used to enable or disable the lower ROM area. The lower ROM area occupies memory addresses &0000-&3fff and is used to access the operating system ROM. When the lower ROM area is is enabled, reading from &0000-&3FFF will return data in the ROM. When a value is written to &0000-&3FFF, it will be written to the RAM underneath the RAMROM. When it is disabled, data read from &0000-&3FFF will return the data in the RAM.
Similarly, bit 3 controls enabling or disabling of the upper ROM area. The upper ROM area occupies memory addressess &C000-&FFFF and is BASIC or any expansion ROMs which may be plugged into a ROM board/box. See the document on [[Upper ROM Bank Number|upper rom selection]] for more details. When the upper ROM area enabled, reading from &c000-&ffff, will return data in the ROM. When data is written to &c000-&FFFF, it will be written to the RAM at the same address as the ROM. When the upper ROM area is disabled, and data is read from &c000-&ffff it will be the data in the RAM.
Bit 4 controls the interrupt generation. It can be used to delay interrupts. See the document on interrupt generation for more information.
==== Summary ====
=== Register MMR (RAM memory mapping) ===
This register exists only in CPCs with 128K RAM (like the CPC 6128), or CPCs equipped with [[Standard Memory Expansions]]). Note: In the CPC 6128, the register is a separate [[PAL16L8|PAL chip]] that assists the Gate Array chip. See its wiki page.
{| class="wikitable"
=== Green Screen Colours ===
On a green screen (, where all colours are shades of unsaturated green), the colours (in BASIC colours) are in order of increasing intensity. Black is very darkdarkest green, and white is bright brightest green, and colour 13 is a medium green. (Thanks to [[Mark Rison|Mark Rison]] for this information)
The luminance (Y) is not exactly correlated to the actual luminance of colour images broadcast in RGB. We have other values.