| SYMBOL | PIN | DESCRIPTION |
| P3O - P3.7 | 41 - 48 | 8-bit quasi-bidirectional l/0 port Port pin Alternative function P3.0 RXD : Serialinput port P3.1 TXD : Serialoutput port P3.2 INTO : Externalinterrupt P3.3 INTl : Externalinterrupt P3.4 TO : Timero externalinput P3.5 T1 : Timer l externalinput P3.6 WR : External data memory write strobe P3.7 RD : External data memory read strobe |
| N.C | 49 - 50 | Not connected pins. |
| XTAL2 | 51 | C rystal pin 2: output of the inve rting amplifier that fo rms the oscillato r. Left open-circuit when an external oscillator clock is used. |
| XTAL1 | 52 | Crystal pin l: input to the inverting amplifier that forms the oscillator, and input to the internal clock generator. Receives the external oscillator clock signal when an external oscillator is used. Must be connected to logic HIGH if the PLL oscillator is selected (SELXTALl = LOW) |
| P2O - P2.7 | 55 - 62 | Port2: 8-bit quasi-bidirectional l/0 port with internal pull-ups.During access to external memories (RAM/ROM) that use 16-bit addresses (MOVX@DPTR) Port 2 emits the high order address byte. Port 2 can sink/source one TTL (=4 LSTTL) input. It can drive CMOS inputs without external pull-ups. |
| PSEN | 63 | Program Store Enable output: read strobe to the external program memory via Port o and 2. Is activated twice each machine cycle during fetches from external program memory. When executing out of external program memory two activations of PSEN are skipped during each access to external data memory. PSEN is not activated (remains HIGH) during no fetches from external program memory. PSEN can sink/source 8 LSTTL inputs. It can drive CMOS inputs without external pull-ups. |
| ALE/WE | 64 | Address Latch Enable output: latches the low byte of the address during access of external memory in normal operation. It is activated every six oscillator periods except during an external data memory access. ALE/WE can sink/-source 8 LSTTL inputs. It can drive CMOS inputs without an external pull-up. To prohibit the toggling of ALE pin (RFI noise reduction) the bit RFI in the PCON Register (PCON.5) must be set by software. This bit is cleared on RESET and can be set and cleared by software. When set, ALE pin will be pulled down internally, switching an external address latch to a quiet state. The MOVX instruction will still toggle ALE if external memory is accessed. ALE will retain its normal high value during Idle Mode and a low value d u ring Power-down Mode while in the "RFI" mode. Additionally during internal access (EA = 1) ALE will toggle normally when the add ress exceeds the internal program memory size. During external access (EA = 0) ALE will always toggle normally, whether the flag "RFI" is set or not. |
| EA | 65 | External Access Input: If, during RESET, EA is held at a TTL level HIGH the CPU executes out of the internal program memory, provided the program counter is less than 49152. If, during RESET, EA is held at a TTL level LOW the CPU executes out of external program memory via Port o and Port 2. EA is not allowed to float. EA is latched during RESET and don't care after RESET. |
| P0.7-PO.O | 68 -75 | Port 0: 8-bit open drain bidirectional l/0 port. It is also the multiplexed low-order address and data bus during accesses to external memory (during theses accesses internal pull-ups are activated). Port o can sink/source 8 LSTTL inputs. |
| XTAL3 | 78 | Crystal pin, output of the inverting amplifier that forms the 32 kHz oscillator |
| XTAL4 | 79 | Crystal pin, input to the inverting amplifier that forms the 32 kHz oscillator. XTAL3 and XTAL4 are pulled LOW if the PLL oscillator is not selected (SELXTALl = HIGH) or if Reset is active. |
| SELXTAL1 | 80 | Must be connected to logic HIGH level to select the H F oscillator, using the XTALl/XTAL2 crystal. If pulled low the PLL is selected for clocking of the controller, using the XTAL3/ XTAL4 crystal. |
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