diff --git a/apple2gs.equ.S b/apple2gs.equ.S
index 92d4331..cc986ce 100644
--- a/apple2gs.equ.S
+++ b/apple2gs.equ.S
@@ -7,6 +7,10 @@ KBD		equ $c000
 VGCINT		equ $c023
 SCANINT		equ $c032
 
+RDCARDRAM	equ $c003
+RDMAINRAM	equ $c002
+WRCARDRAM	equ $c005
+WRMAINRAM	equ $c004
 
 * modem port / printer port
 
@@ -27,3 +31,4 @@ IRQ1SEC		equ $e10054
 IRQQTR		equ $e10038
 IRQVBL		equ $e10030
 IRQSND		equ $e1002c
+
diff --git a/vt100.modem.S b/vt100.modem.S
index 385542b..fe84473 100644
--- a/vt100.modem.S
+++ b/vt100.modem.S
@@ -14,6 +14,16 @@ SCCBDATA	equ $c03a
 SCCADATA	equ $c03b
 
 
+*
+* scc speed:
+* 
+* time constant = ( clock / (2 * clock mode * baud rate)) - 2
+* baud rate = clock / ( 2 * clock mode * (time constant + 2))
+*
+* clock mode = 1x, 16x, 32x, or 64x (selected via write register 4 bits 6/7)
+* clock = 3.6864 MHz crystal (scc runs at 14.31818 / 4 = ~ 3.58 Mhz)
+* time constant = write register 12 (low) + 13 (high)
+
 
 init_modem ent
 *	sep #$30