Update ReadMe.md

Author: lynchaj

Z80SERIAL2/ReadMe.md

@@ -19,3 +19,20 @@ Interrupt LED
 Receive and Transmit LEDs
 
 Default IO port $68-$6F
+
+# Jumpers
+
+J1 Interrupt Select, connect 1-2 for INT# default, connect 2-3 for NMI#, none for no interrupt
+Note: can connect J1 pin 2 via flying lead to Z80 processor IM2 connector
+
+J2 is Ring Indicator input option.  Pins 1-2 closed (default) for RI# set to VCC (inactive) as default.  Pins 2-3 closed to export RI# to experiment connector J9
+
+J3 is Carrier Detect input option.  Pins 1-2 closed (default) for DCD# set to GND (active) as default.  Pins 2-3 closed to export DCD# to experiment connector J9
+
+J7 TTL Level Serial Ports Power, connect 1-2 for Port Power, default is none
+
+J8 is TTL Serial port option CTS# or DSR#.  Depending on TTL Serial to USB adaptor can go either way.  Pins 1-2 closed is CTS# (default), pins 2-3 closed is DSR#, no jumper is none.
+
+JP1 is connector for external recovery switch (on-momentary) not a jumper.  Do not install jumper
+
+J5 is External DMA interface circuit connector.  Do not install jumpers on J5 as it is meant for external cable.