Changes
== LK1,LK2,LK3 - Manufacturer ID ==
LK1,LK2,LK3 connect to [[8255|PPI]] Port B, Bit1-3. The links select the manufacturer name (which is displayed by the BIOS in the power-up message). These LKs exist on all CPC mainboards (in CPC Plus/GX4000 schematics they are named LK101,LK102,LK103).
== LK4 - Screen Refresh Rate ==
LK4 connects to [[8255|PPI]] Port B, Bit4. The link tells the BIOS whether it should set-up the [[CRTC]] for 50Hz or 60Hz refresh rate.
== CPC6128 : LK5,LK6,LK8 - Disable 128K RAM Banking ==
The CPC6128 contains 128K RAM, RAM banking is controlled by a PAL (which assists its [[Gate Array]]). However, the 6128 mainboard can be also used for 64K computers - in that case, only 64K would be installed, the PAL would be missing, and LK5,LK6,LK8 would be installed (bypassing the RAM banking logic, and passing signals directly to unbanked RAM). The CPC+ has a similar feature (see R128 below).
== DDI-1 : LK1 - Autoboot CP/M ==
In the DDI-1, LK1 connects '''both''' to the Expansion Port /EXP pin (which goes to [[8255|PPI]] Port B, Bit5, '''and''' to the AMSDOS ROM bank number selection logic. The latter one allow to map AMSDOS to bank 7 (default), or bank 0. If AMSDOS sees itself mapped to bank 0, then it does automatically load & start the boot sector from drive A (equivalent as when typing |CPM after power-up).
== DDI-1 : LK2,LK3 - Disc Low-Level Stuff or so ==
In DDI-1, LK2-LK3 connect to the Disc Data Separator. Purpose...?
== CPC6128 : LK7 - Autoboot CP/M ==
== CPC Plus : R128,R129,R130 LK105 - Autoboot CP/M ==
Same as DDI-1:LK1 (see there). == CPC Plus:R128 (10kOhm) - 128K RAM Enable == Installed for 128K DRAM, not installed for 64K DRAM. == CPC Plus:R129 (10kOhm) - Disc Vers Enable == '''Purpose Unknown !!!'''* The ASIC (where R129 connects to) should hava nothing to do with the FDC. However, it does control the AMSDOS ROM bank selection: translating ROM bank 7 (or 0) to cartridge bank 3.* Possibly, removing R129 might disable that feature (so cartridge bank 3 could be only accessed as ROM bank 83h, but not as ROM bank 7, nor 0.This is not verified, can somebody test what happens when installing/removing R129 ? == CPC Plus:R130 (10kOhm) - 8bit Printer Enable == When installed (default), enables the 8th printer bit, controlled via [[CRTC]]. When removed, outputs LOW as 8th bit (as on classic CPCs with 7bit printer port). See also: [[8bit Printer Ports]]. == CPC Plus Cartridges : LK1-LK6 - EPROM Address Lines ==
