Resolve #471 (although link code still needs more cleanup, like its WRAM labels)

constants/serial_constants.asm

@@ -6,7 +6,25 @@
 	const LINK_COLOSSEUM   ; 3
 	const LINK_MOBILE      ; 4
 
-
+; hSerialReceive high nybbles
 SERIAL_TIMECAPSULE EQU $60
 SERIAL_TRADECENTER EQU $70
 SERIAL_BATTLE      EQU $80
+
+ESTABLISH_CONNECTION_WITH_INTERNAL_CLOCK EQU $01
+ESTABLISH_CONNECTION_WITH_EXTERNAL_CLOCK EQU $02
+
+START_TRANSFER_EXTERNAL_CLOCK EQU $80 ; 1 << rSC_ON
+START_TRANSFER_INTERNAL_CLOCK EQU $81 ; (1 << rSC_ON) | 1
+
+; hSerialConnectionStatus
+USING_EXTERNAL_CLOCK       EQU $01
+USING_INTERNAL_CLOCK       EQU $02
+CONNECTION_NOT_ESTABLISHED EQU $ff
+
+; signals the start of an array of bytes transferred over the link cable
+SERIAL_PREAMBLE_BYTE              EQU $fd
+; this byte is used when there is no data to send
+SERIAL_NO_DATA_BYTE               EQU $fe
+; signals the end of one part of a patch list (there are two parts) for player/enemy party data
+SERIAL_PATCH_LIST_PART_TERMINATOR EQU $ff