diff --git a/main.s b/main.s
index 411a172..2575e54 100644
--- a/main.s
+++ b/main.s
@@ -9,7 +9,7 @@ CHIP SN8F2288
 	.Code_Option	Reset_Pin	"P07"
 	.Code_Option	Rst_Length	"No"
 	.Code_Option	Security	"Enable"
-	.Code_Option	Watch_Dog	"Enable"
+	.Code_Option	Watch_Dog	"Enable"  ; On except for Green/Powerdown modes
 //}}SONIX_CODE_OPTION
 
 .DATA
@@ -405,8 +405,77 @@ _mainloop:
 	JMP _usb_reset
 	B0BTS0 FSOF
 	JMP _usb_sof
+	B0BTS0 FSUSPEND
+	JMP _usb_suspend
 	JMP @B
 
+_usb_suspend:
+	MOV A, #'P'
+	CALL _uart_tx
+	MOV A, #'D'
+	CALL _uart_tx
+
+	; enter suspend
+	B0BCLR 0xa9.4 ; Switch UTX to INPUT
+	B0BCLR P5M.3  ; Disable power LED
+
+	; output low on sense lines
+	B0BSET S0M
+	B0BSET S1M
+	B0BSET S2M
+	B0BSET S3M
+	B0BSET S4M
+	B0BSET S5M
+	B0BSET S6M
+	B0BSET S7M
+	B0BSET S8M
+	B0BSET S9M
+	B0BSET S10M
+	B0BSET S11M
+	B0BSET S12M
+	B0BSET S13M
+	B0BSET S14M
+	B0BSET S15M
+
+	B0BSET FCPUM0 ; Enter sleep mode
+	NOP
+	NOP
+
+	; exit suspend
+	CALL _gpio_init
+	B0BSET 0xa9.4 ; Switch UTX to UART
+
+	; did host wake us?
+	B0BTS1 FSUSPEND
+	JMP @F
+
+	; key-press wake?
+	MOV A, #'!'
+	CALL _uart_tx
+
+	; Signal K state to wake host
+
+	; Drive D+ low, D- high (K state)
+	MOV A, #0x05
+	B0MOV UPID, A
+	; FIXME: Wait at least 1ms, no longer than 15ms
+	CALL _delayshort
+	CALL _delayshort
+	CALL _delayshort
+	CALL _delayshort
+	CALL _delayshort
+	CALL _delayshort
+	; Revert back to default
+	MOV A, #0x00
+	B0MOV UPID, A
+
+@@:
+	MOV A, #'W'
+	CALL _uart_tx
+	MOV A, #'U'
+	CALL _uart_tx
+	JMP _mainloop
+
 _usb_sof:
 	B0BCLR FSOF
 
@@ -510,6 +579,8 @@ _gpio_init:
 	B0MOV P2UR, A
 	B0MOV P4UR, A
 	B0MOV P5UR, A
+	; Enable P1 wakeup
+	B0MOV P1W, A
 	; Switch all to input
 	MOV A, #0x00
 	B0MOV P0M, A
diff --git a/pinout.txt b/pinout.txt
index 1de0216..26faa47 100644
--- a/pinout.txt
+++ b/pinout.txt
@@ -105,3 +105,22 @@ INTERNATIONAL4             F7              O             F8              L
         (none)           LGUI    KP_MEMCLEAR         (none)         (none)            F12         (none)          RIGHT   P4.7/S13
             UP    KP_MEMSTORE         (none)         (none)             FN            END          PAUSE           LEFT   P0.3/S14
         (none)         (none)         (none)         DELETE    PRINTSCREEN         INSERT         PAGEUP       PAGEDOWN   P0.6/S15
+
+Suspend/Resume notes:
+- In FS mode, if IDLE (J state) is held for more than 3ms without SOF,
+  this signals SUSPEND. During suspend J state is kept. D+ pullup
+  continues to be powered.
+- Suspend current should be less than 2.5mA (including pullup/pulldowns)
+- Wakeup is signalled by either device or host by changing to K state
+  (min 1ms, max 15ms for device-caused wakeup)
+- Thus, UPID register can be used to temporarily override D+/D- state to
+  signal a RESUME request to the host
+- In powerdown, DS claims the SN8 can be woken by P0/P1 level change or USB bus
+  toggle, though maybe just P1 since there is only the P1W wake control
+  register
+- P1 would allow any key to wake the uC, assuming GPIO state is kept
+  during power-down:
+  Just enable pull-ups on P1, set Sn gpios to output low value, enable
+  P1W for all Rn.
+- Suitable modes: Slow mode, sleep mode, slow clock green mode (all at 250uA max)
+- Unsuitable modes: Normal mode (10mA), fast clock green mode (5mA)