collapseos/arch/z80/sms/blk/622

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: (spie) DROP ; ( always enabled )
: (spix) ( x -- x, for port B )
0 SWAP ( rx tx ) 8 0 DO
( send bit 7 to bit 6, TR's output bit )
DUP 1 RSHIFT 0x40 AND ( rx tx bits ) 0x80 OR ( CLK hi )
0x3f PC@ OR 0xf3 AND ( TH and TR output )
DUP 0x3f PC! ( rx tx bits )
( CLK low ) 0x7f AND 0x3f PC! ( rx tx )
( shift tx ) 1 LSHIFT ( rx tx<< )
( read into rx ) SWAP 1 LSHIFT 0xdc PC@ ( tx<< rx<< x )
( out bit is the 6th ) 6 RSHIFT 1 AND OR
SWAP LOOP ( rx tx ) DROP ;