DMG-CPU SM83 Core Connections

This is a list of all connections to/from the SM83 CPU core as seen in the Gameboy DMG-CPU-B die shot. It builds on the work of Furrtek, the information found in his DMG-CPU-Inside repository.

Please report any errors I made here.

SM83 "Pinout"

SM83 CPU core inside Game Boy DMG-CPU B chip

SM83 Connections

I/O Wire Cell Description
T1 O FROM_CPU6 LEXY.in The output of the inverter LEXY ends at an output pad at the bottom of the die, which is not bonded.
T2 I TO_CPU BOWA.q A gated 1 MiHz clock. The CPU can stop this clock by driving T11 or T14 low. This is the inverse of T3.
T3 I unlabeled BEDO.q A gated 1 MiHz clock. The CPU can stop this clock by driving T11 or T14 low. This is the inverse of T2.
T4 I unlabeled BEKO.q, BAVY.q A gated 1 MiHz clock. The CPU can stop this clock by driving T11 low. This is the inverse of T5.
T5 I PHI_OUT BUDE.q, BEVA.q A gated 1 MiHz clock. This is the inverse of the clock that comes out of the PHI pin of the chip. (PHI_OUT is connected to the output buffer of the PHI pin, but the output buffer is inverting.) The CPU can stop this clock by driving T11 low. This is the inverse of T4.
T6 I unlabeled BOLO.q, BYDA.q A gated 1 MiHz clock. The CPU can stop this clock by driving T11 low. This is the inverse of T7.
T7 I FROM_CPU5 BUFA.q, BYLY.q NOTE: The label used in the schematics is misleading. This is not FROM CPU; it is TO CPU!
A gated 1 MiHz clock. The CPU can stop this clock by driving T11 low. This is the inverse of T6.
T8 I unlabeled BUKE.q A gated 1 MiHz clock. The CPU can stop this clock by driving T11 low.
T9 I unlabeled BOMA.q A gated 1 MiHz clock. The CPU can stop this clock by driving T14 low. This is the inverse of T10.
T10 I BOGA1MHZ BOGA.q A gated 1 MiHz clock. The CPU can stop this clock by driving T14 low. This is the inverse of T9.
T11 O CLK_FROM_CPU ABOL.in, TUBO.in1 NOTE: The label used in the schematics is misleading. This is not a clock!
CPU can drive this low to disable most of the clocks fed to itself. T9 and T10 are the only clocks that are not turned off when this signal gets driven low. However, T9 and T10 might have slightly shorter "shorter" phases while this signal is high. By "shorter" phases I mean, they are not symetric and have a shorter and a longer phase (and the shorter one gets even shorter). This is because of BUTO mixing them with the other clocks when they're active. Maybe they did this to guarantee a specific synchronicity between T9/T10 and the other clocks that tick at around the same time as T9/T10.
The initial state (during and directly after reset) of T11 must be low. The CPU must NOT switch this signal to high immediately after reset, otherwise the synchronous CPU reset T12 (AFER) and the synchronous peripheral resets (RESET2, RESET6, RESET7, ...) will never be deasserted. The CPU must wait until T15 (TABA) gets high. This happens when the DIV register is half run through, which takes about 32 milliseconds. Then the CPU can pull T11 high, which deasserts the synchronous CPU and peripheral resets one T9/T10 tick later. Wether the CPU pulls T11 high immediately when T15 gets high or if it delays that by a T9/T10 tick is unknown (both will work fine). I assume this mechanism is there to assure the crystal oscillator is stabilized.
The same mechanism likely is used when the system wakes up from STOP mode. When the crystal oscillator gets disabled by driving T14 low, the DIV register gets reset to zero, so it will take the same ~32 ms.
For this mechanism to work, many of the bugs in the schematics must be fixed, especially #29, #10 and #43.
When the CPU executes a HALT instruction and none of the enabled interrupts are pending, then the CPU will pull T11 low to disable most of its clocks. When waking up from HALT mode (due to an interrupt), the CPU will pull T11 high on the next T9/T10 tick, which re-enables all the other clocks.
T12 I unlabeled AFER.q Active-high synchronous reset input. Synchronized to T9/T10.
T13 I RESET RST (ext. pad) Active-high asynchronous reset input. Fed directly from RST input pad.
T14 O CLKIN_A multiple NOTE: The label used in the schematics is misleading. This is not a clock; nor is it an input!
Crystal oscillator enable. When CPU drives this low, the crystal oscillator gets disabled to save power. This happens during STOP mode.
T15 I unlabeled TABA.q Active-high crystal oscillator stablilized input? After reset, this signal gets high after about 32 milliseconds. The CPU must not drive T11 high before T15 gets high. See description of T11.
T16 I unlabeled (ext. pad) Directly connected to an input pad at the top of the die, which is not bonded.
R1 O CPU_RAW_RD multiple Active-high memory RD signal from CPU.
R2 O FROM_CPU3 multiple Active-high memory WR signal from CPU.
R3 I T1T2 UNOR.q Maybe used to disable all bus drivers in the CPU when test mode is active.
R4 I unlabeled SYRO.q High when address bus is 0xfexx or 0xffxx. When high, it suppresses R7, so that the data bus can be driven by an internal component (HRAM, OAM, FFxx registers). I suspect this is also used by the CPU to decode the address for the interrupt enable register (0xffff), but I'm not sure yet.
R5 I unlabeled TUTU.q High when address bus is 0x00xx and boot ROM is still visible. When high, it suppresses R7, so that the data bus can be driven by the internal boot ROM.
R6 I T1T2 UMUT.q Maybe used to disable all bus drivers in the CPU when test mode is active.
R7 O FROM_CPU4 TEXO.in1, AGUT.in3 Active-high external memory request. Has to be high during external memory cycles (read or write). This causes one of the chip select signals (CS, MCS, A15) to be asserted in the right moment. Has to be low if no memory cycle is going on, otherwise the chip select will be asserted even if R1 and R2 are low. During write cycles, this signal is also needed for driving the internal data bus onto the I/O pads. During read cycles, this signal is also needed for latching the I/O pads and driving the latched data onto the internal data bus. When R4 or R5 is high, the CPU keeps this signal low, allowing internal components (HRAM, OAM, boot ROM, FFxx registers) to drive the internal data bus.
R8 ? - - Not connected.
R9 ? - - Not connected.
R10 ? - - Not connected.
R11 ? - - Not connected.
R12 ? - - Not connected.
R13 ? - - Not connected.
R14 O CPU_IRQ0_ACK LETY.in Active-high. Acknowledges IRQ0 (V-Blank).
R15 I CPU_IRQ0_TRIG LOPE.q Active-high. Triggers IRQ0 (V-Blank).
R16 O CPU_IRQ1_ACK LEJA.in Active-high. Acknowledges IRQ1 (Status).
R17 I CPU_IRQ1_TRIG LALU.q Active-high. Triggers IRQ1 (Status).
R18 O CPU_IRQ2_ACK LESA.in Active-high. Acknowledges IRQ2 (Timer).
R19 I CPU_IRQ2_TRIG NYBO.q Active-high. Triggers IRQ2 (Timer).
R20 O CPU_IRQ3_ACK LUFE.in Active-high. Acknowledges IRQ3 (Serial).
R21 I CPU_IRQ3_TRIG UBUL.q Active-high. Triggers IRQ3 (Serial).
R22 O CPU_IRQ4_ACK LAMO.in Active-high. Acknowledges IRQ4 (Joypad).
R23 I CPU_IRQ4_TRIG ULAK.q Active-high. Triggers IRQ4 (Joypad).
R24 O CPU_IRQ5_ACK - Active-high. Acknowledges IRQ5. Not connected.
R25 I CPU_IRQ5_TRIG GND Active-high. Triggers IRQ5. Hardwired to GND.
R26 O CPU_IRQ6_ACK - Active-high. Acknowledges IRQ6. Not connected.
R27 I CPU_IRQ6_TRIG GND Active-high. Triggers IRQ6. Hardwired to GND.
R28 O CPU_IRQ7_ACK - Active-high. Acknowledges IRQ7. Not connected.
R29 I CPU_IRQ7_TRIG GND Active-high. Triggers IRQ7. Hardwired to GND.
B1 I/O D0 multiple Data bus D0.
B2 I/O D1 multiple Data bus D1.
B3 I/O D2 multiple Data bus D2.
B4 I/O D3 multiple Data bus D3.
B5 I/O D4 multiple Data bus D4.
B6 I/O D5 multiple Data bus D5.
B7 I/O D6 multiple Data bus D6.
B8 I/O D7 multiple Data bus D7.
B9 O A15 multiple Address bus A15.
B10 O A14 multiple Address bus A14.
B11 O A13 multiple Address bus A13.
B12 O A12 multiple Address bus A12.
B13 O A11 multiple Address bus A11.
B14 O A10 multiple Address bus A10.
B15 O A9 multiple Address bus A9.
B16 O A8 multiple Address bus A8.
B17 O A7 multiple Address bus A7.
B18 O A6 multiple Address bus A6.
B19 O A5 multiple Address bus A5.
B20 O A4 multiple Address bus A4.
B21 O A3 multiple Address bus A3.
B22 O A2 multiple Address bus A2.
B23 O A1 multiple Address bus A1.
B24 O A0 multiple Address bus A0.
B25 I TO_CPU2 AWOB.q Wakes CPU from STOP mode.