squk / gba-lcd

Reverse engineered documentation on the Game Boy Advance(GBA) LCD Interface

Game Boy Advance(GBA) LCD Interface

Manufactured by Sharp. Potential model numbers: LQU29B2DDO2P 18H00862812 or QPWBH2218TPZZ. Data-sheets unavailable.

40-Pin FFC Pinout

Pin	Name	Description	Details
1	TST2
2	VSHD
3	DCLK	Pixel clock	Active on negative edge
4	LP	Data latch of signal source driver (i.e pixel clock)	Active on positive edge
5	PS	Power save signal	Active on positive edge
6	DGND	Digital ground
7	VSHD
8	LDR5	Bit 4 of digital red
9	LDR4	Bit 3 of digital red
10	LDR3	Bit 2 of digital red
11	LDR2	Bit 1 of digital red
12	LDR1	Bit 0 of digital red
13	LDG5	Bit 4 of digital green
14	LDG4	Bit 3 of digital green
15	LDG3	Bit 2 of digital green
16	LDG2	Bit 1 of digital green
17	LDG1	Bit 0 of digital green
18	LDG0	Labeled as bit 0 of digital green, but tied to ground	GND
19	LDB5	Bit 4 of digital blue
20	LDB4	Bit 3 of digital blue
21	LDB3	Bit 2 of digital blue
22	LDB2	Bit 1 of digital blue
23	LDB1	Bit 0 of digital blue
24	SPL	Sampling start signal (HSYNC)	Active on positive edge
25	CLS	Clock signal of gate driver
26	SPS	Start signal of gate driver. f = 59.737Hz/ (i.e. VSYNC)	Active on negative edge
27	TST
28	MOD	Control signal of gate driver
29	VCOM	Common electrode driving signal	Active on positive edge
30	VEE
31	VSS
32	VCC
33	-
34	VSHA
35	AGND	Analog ground
36	V4	Voltage provided by AGB-REG chip on 40-pin GBA models. Check service manual.	Vpp=3.00V at 6.81KHz
37	V3	Voltage provided by AGB-REG chip on 40-pin GBA models. Check service manual.	Vpp=2.32V at 6.81KHz
38	V2	Voltage provided by AGB-REG chip on 40-pin GBA models. Check service manual.
39	V1	Voltage provided by AGB-REG chip on 40-pin GBA models. Check service manual.	Vpp=3.72V at 6.81KHz
40	V0	Voltage provided by AGB-REG chip on 40-pin GBA models. Check service manual.	Vpp=3.60V at 6.81KHz

Signals Explained

The delta between the two cursors(neg edge of SPS) here is 16.743 ms, with a frequency averaging 59.728Hz, i.e. the refresh rate of the GameBoy Advance, indicating this is likely our VSYNC signal:

Zooming in, we can see that LP, PS, and SPL are all pulses that are active on the negative edge and each seem to represent the beginning of a pixel(each negative edge of the DCLK signal represents 15-bits of RGB being read by the display):

However, the PS signal is changed from a positive duty cycle of 85.699% to a positive duty cycle of 6.498% during the VBLANK period(SPS pulse followed by SPL pulse is the first pixel of the frame). This duty cycle change is shown here:

Resources

Portuguese GBA internal service manual

Contains acronyms for most of the 40-pins present on the Game Boy. This was super helpful when I was having trouble figuring out why my signals suddenly made no sense(my FFC was upside-down).
https://dragaosemchama.com/wp-content/uploads/2015/02/GBA-service-Manual.pdf

AlexiG's blog post

Great explanation of some of the LCD interface's signals. Wish I had found this sooner:
https://www.insidegadgets.com/2019/08/08/playing-around-with-the-gba-lcd/

Sharp LQ035Q7DH07 TFT-LCD Datasheet

An LCD datasheet from the same manufacturer as the GBA, although the LCD in the datasheet was manufactured 5-6 years after the Game Boy Advance.
https://www.mouser.com/datasheet/2/365/LQ035Q7DH07N_SPEC_LD-21910A-184021.pdf