Serial I/O

A MC68B50 Asynchronous Communications Interface Adapter (ACIA) gives the RC2014 the ability to talk to the outside world through a serial port.  This board is designed to either be used with a 5v FTDI lead (which can also power the RC2014), or optionally through a full RS232 serial cable.

Serial

The 68B50 is run from the same clock as the Z80, which with a 7.3728Mhz crystal will communicate at 115200 baud.  If a 3.6864 Mhz crystal is used, the baudrate drops to 57600, but you will be able to use the cheaper (and slightly easier to get hold of) 6850 ACIA.

If you plan to only communicate over 5v TTL serial (such as via an FTDI lead, or with a modern micro like an Arduino), then you will not need to fit the MAX232, capacitors or 9 pin D socket.  This part of the circuit simply boosts and inverts the 5v serial to full 12v RS232 standard.

If the RC2014 is being powered from an FTDI lead, then the “5v FTDI” jumper should be in place.  Otherwise, remove it.  Note that with just the bare essentials (CPU, ROM, RAM, IO and Clock), the RC2014 pulls around 200ma, which is well within the 350ma or so that most FTDI leads can supply.

Both the Tx and Rx lines are presented on the pins to the back plane (Pins 35 & 36), so building additional interfaces to communicate with this is straight forward.

Scm_SerialIO

Note that the 63B50 is functionally equivalent to the 68B50 and can be used interchangeably.

SerialIO_Tindie

Buy one here

Bill of materials

  • 36 pin RA Header
  • 24 pin wide DIL socket
  • 14 pin narrow DIL socket
  • MC68B50
  • 74LS04
  • 6 pin header
  • 2 pin header
  • 2k2 resistor

Optional additional materials for RS232

  • 16 pin narrow DIL socket
  • MAX232
  • 1uf 25v electrolytic
  • 9 pin D socket

 

2 Comments
  1. […] Serial -a 68B50 supported by a 74HCT04 with headers for an FTDI cable (and space for a 232Max chip for those wanting RS-232) […]

  2. […] the 7.3728MHz Z80 processor to handle. Unfortunately neither the MC68B50 ACIA used on the original RC2014 Serial I/O module nor the Z80 SIO used on the current Dual Serial SIO/2 module has an internal baud rate […]