Header JP2 has a UART populated UART:
Pins functions are marked.
------------------ Board Configuration ------------------ **************************** GS1900-8 **************************** ============================ Board GPIO ============================ Device Pin Direction Default Current ------- ---- ---------- -------- -------- INT 0 OUT 0 0 INT 1 OUT 1 1 INT 2 OUT 0 0 INT 3 OUT 0 0 INT 8 OUT 1 1 INT 9 OUT 1 1 INT 12 IN 0 0 INT 13 OUT 1 1 INT 14 OUT 1 1 INT 15 OUT 1 1 INT 16 IN 0 0 INT 17 OUT 1 1 INT 18 OUT 0 0 INT 19 IN 0 0 INT 20 OUT 1 1 INT 21 IN 0 0 INT 22 IN 0 0 INT 23 OUT 1 1 EXT 0 IN (IN ) 0 0 EXT 1 IN (IN ) 0 0 EXT 2 IN (IN ) 0 0 EXT 3 IN (IN ) 0 1 EXT 4 IN (IN ) 0 0 EXT 5 OUT (OUT ) 1 1 EXT 6 OUT (OUT ) 1 1 EXT 7 IN (IN ) 0 1 EXT 8 OUT (OUT ) 1 1 EXT 13 OUT (OUT ) 0 0 EXT 14 OUT (OUT ) 0 0 EXT 15 OUT (OUT ) 0 0 EXT 16 OUT (OUT ) 0 0 EXT 17 OUT (IN ) 0 0 EXT 18 OUT (IN ) 0 0 EXT 22 IN (IN ) 0 0 EXT 23 OUT (OUT ) 0 0 EXT 24 OUT (OUT ) 0 0 EXT 25 OUT (OUT ) 0 0 EXT 26 IN (IN ) 0 0 EXT 27 IN (IN ) 0 0 EXT 28 IN (IN ) 0 0 EXT 29 OUT (OUT ) 0 0 EXT 30 OUT (OUT ) 0 0 EXT 31 OUT (OUT ) 0 0 EXT 32 IN (IN ) 0 0 EXT 33 IN (IN ) 0 0 EXT 34 OUT (OUT ) 1 1 ============================ Board Configuration ============================ ====== Port ================== Type Usr Phy Media Speed Duplex Attr ---------- ---- ------- ----------- -------------- -------- ------- 1000M 1 (0) 8 Copper (A) ALL Auto 0 1000M 2 (0) 9 Copper (A) ALL Auto 0 1000M 3 (0) 10 Copper (A) ALL Auto 0 1000M 4 (0) 11 Copper (A) ALL Auto 0 1000M 5 (0) 12 Copper (A) ALL Auto 0 1000M 6 (0) 13 Copper (A) ALL Auto 0 1000M 7 (0) 14 Copper (A) ALL Auto 0 1000M 8 (0) 15 Copper (A) ALL Auto 0 ====== Button ================ ------------ Reset Button GPIO: EXT_3 Timer: 3(sec) Action: Reboot Timer: 6(sec) Action: Restore Factory ====== Led =================== SYS (REG) ALARM (REG) ====== Reset ================= Type: GPIO GPIO: EXT_5 ====== WatchDog ============== Type: REG