int e l 10.2 EPROM PROGRAMMING CONFIGURATION/TIMING P1.4 -- PROGRAM PULSE WIDTH PORT 1, BIT 4 (pin 5 on the 8052AH) is used to provide the 50 millisecond or the 1 millisecond programming pulse. The length of the programming pulse is determined by whether the "normal" or the "INTELligent" EPROM programming mode is selected. MCS BASIC-52 calculates the length of the programming pulse from the assigned crystal value. So, be sure the proper XTAL has been assigned. The accuracy of this pulse is within 10 CPU clock cycles. This pin is normally in a logical high (1) state. It is asserted low (0) to program the EPROMS.
Depending on the EPROM to be programmed this signal will be used in different ways. More about this later. P1.5 -- ENABLE PROGRAM VOLTAGE PORT 1, BIT 5 (pin 6 on the 8052AH) is used to enable the EPROM programming voltage. This pin is normally in a logical high (1) state. Prior to the EPROM programming operation, this pin is brought to a logical low (0) state. This pin is used to turn on or off the high voltage (12.5 volts to 25 volts, depending on the EPROM) required to program the EPROMS. The timing for the EPROM programming pins is shown in figure 3. The hardware required to program different devices is shown in figure 4.
Note that with very little external hardware the MCS BASIC-52 device can program virtually all commercially available EPROMS. Additionally, figure 5 suggests a circuit using an INTEL 2816A EEPROM. This circuit also features a push button erase option. IMPORTANT NOTE MCS BASIC-52 calculates the programming pulse width when the XTAL value is assigned. To insure proper programming, make sure XTAL is assigned the proper value. MCS BASIC-52 performs the pro- gramming pulse width calculation to within 5 clock cycles, so the accuracy of the programming pulse is well within the limits of any EPROM device.
10.3 SERIAL PORT IMPLEMENTATION The serial port I/O signals on the 8052AH are TTL compatible signals. They are typically not compatible with most terminals. Figure 6 suggests hardware options for making the serial interface compatible with terminals. The serial port is initialized by MCS BASIC-52 to the 8-bit uart mode. In this mode 8 data bits, plus one start and one stop bit are transmitted. Parity is not used. - 136 -