Chapter 3: Hardware
V104
3-6
This returns an 8-bit value for each port, with each bit corresponding to the appropriate line on the port.
You will find that numerous on-board components are controlled using PPI lines only. You will need to use
PPI access methods to control these, as well.
The V104 J5 header pin layout is as follows:
Pin 1 = I10
Pin 2 = GND
Pin 3 = I11
Pin 4 = GND
Pin 5 = I12
Pin 6 = GND
Pin 7 = I13
Pin 8 = GND
Pin 9 = I14
Pin 10 = GND
Pin 11 = I15
Pin 12 = GND
Pin 13 = I16
Pin 14 = GND
Pin 15 = I17
Pin 16 = GND
Pin 17 = I20
Pin 18 = GND
Pin 19 = I21
Pin 20 = GND
Pin 21 = I22
Pin 22 = GND
Pin 23 = I23
Pin 24 = GND
Pin 25 = I24
Pin 26 = GND
Pin 27 = I25
Pin 28 = GND
Pin 29 = I26
Pin 30 = GND
Pin 31 = I27
Pin 32 = GND
Pin 33 = I00
Pin 34 = GND
Pin 35 = I01
Pin 36 = GND
Pin 37 = I02
Pin 38 = GND
Pin 39 = I03
Pin 40 = GND
Pin 41 = I04
Pin 42 = GND
Pin 43 = I05
Pin 44 = GND
Pin 45 = I06
Pin 46 = GND
Pin 47 = I07
Pin 48 = GND
Pin 49 = VCC
Pin 50 = GND
For more information on this device, please refer to the NEC uPD71055 datasheet (415-960-6000).
3.3.3
RTC72421
A real-time clock RTC72421 (EPSON, U4) is mapped in the I/O address space 0x8000-0xbffff. It must be
backed up with a lithium coin battery. The RTC may be accessed via software drivers rtc_init() or rtc_rd();
(see Chapter 4). Details are listed in Appendix D.
3.3.4
UART SCC2691
The UART SCC2691 (Signetics, U8) is mapped in the I/O address space 0xc000-0xc0ff. The SCC2691 has
a full-duplex asynchronous receiver/transmitter, a quadruple buffered receiver data register, an interrupt
control mechanism, programmable data format, selectable Baud rate for the receiver and transmitter, a
multi-functional and programmable 16-bit counter/timer, an on-chip crystal oscillator, and a multi-purpose
input/output including RTS and CTS mechanism. For more information, refer to Appendix C. The
SCC2691 on the V104 may be used as a network 9th-bit UART. The RxD and TxD signals are routed to the
J2 header for connecting to a VE232. Use J1 pin 3 (RS485-) and pin 4 (RS485+) on the VE232 to join the
multi-drop RS485 twist pair network. The MPO and MPI are routed to J9 of the V104.
3.4
Other Devices
3.4.1
MAX691
The MAX691/LTC691 (U6) is a supervisor chip. With it installed, the V104 has several functions that
significantly improve system reliability: