Changes
/* LK4 - Screen Refresh Rate */
[[Category:CPC Internal Components]]
'''Links''' - Amstrad has used a number of LKs (Links) on CPC mainboards and on peripherals like DDI-1 and CPC+ Cartridges. The LKs are simply a piece of wire that is (or is not) installed between two soldering points.
== 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 /Costdown schematics they are named LK101,LK102,LK103). By default, LK1-LK3 are not installed ([[Amstrad]]). Other combinations are LK2 installed in german [[Schneider]] models, and LK1+LK2 in australian [[Awa]] models. For more info see [[LK-selectable Brand Names]].
== LK4 - Screen Refresh Rate ==
LK4 (LK104 on Plus/GX4000/Costdown) 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. Default is LK4 not installed (50Hz). It might be installed in US models, there isn't too much known about whether CPCs were exported to USA.... One source says that the CPC6128 was initially sold ''only'' in USA... Another source says that Indescomp (spanish distributor) produced CPCs with ''Indescomp International U.S.A.'' stickers. The 60Hz setting may cause compatibility problems with various non-BIOS software. And, due to a BIOS glitch, even with BIOS-based software (see [[Media:S968ap13.pdf|SOFT 968 Appendix 13 (XIII) (Hints Tips and Workarounds)]] for details).
== CPC6128:LK5,LK6,LK8 - Disable 128K RAM Banking ==
== CPC6128:LK7 aka CPC664:LK201 - Autoboot CP/M ==
Same as DDI-1:LK1 (see there). By default, the two soldering points are connected with each other (by a printed wire on the PCB, to activate autoboot one must scratch off that connection).In the CPC664, LK201 is located close to the power-supply connectors.In the CPC6128, LK7 is located close to the gate array.
== CPC Plus:LK105 - Autoboot CP/M ==
== CPC Plus:LK106 - Unknown ==
Purpose unknown...? Usually LK106 is not installed. (related to Upper ROM Bank signals /IORQ, A13, /WAIT, /RESET)
== CPC Plus:R128 aka R28 (10kOhm) - 128K RAM Enable ==
== GX4000:LKs ==
* LK1-LK4 - same as CPC, though not being actually used, due to absent BIOS(though game cartridges could check LK4 to determine the desired video refresh rate) (default is LK1-LK4 not installed, equivalent to Video=50Hz, and Manufacturer=Amstrad)* LK5 - none such...?(corresponding PPI input is floating, neither having a LOW level, nor a stable HIGH level) (meaning the ROM Bank0=BASIC and Bank7=AMSDOS are unstable on GX4000, this seems to be the reason for the CPC+ System Cartridge not booting properly on the GX4000)* LK6 - unknown (same as LK106 on CPC+) (usually LK6 is not installed, neither in GX4000 nor CPC+)* LK7 - shortcut +5V with +5VMOD (use same supply for computer and installed in french version, which has no TV modulator)
