*8252
*serial controller interface (SCC)
*Amongst others from Samsung
*originally probably from Harris
*19891115/wjvg

0 tbr/rbr = transmitter/receiver buffer register
1 ucr/usr = uart control/status register
   w .......0 nr of stopbits = 1
   w .......1 nr of stopbits = 1.5 for 5 bits and 2 for 6,7 or 8 bits
   w ....000. tx par even, rx par even
   w ....001. tx par odd,  rx par odd
   w ....010. tx par even, rx par odd
   w ....011. tx par odd,  rx par even
   w ....100. tx par even, rx no par
   w ....101. tx par odd,  rx no par
   w ....11.. tx no par,   rx no par
   w ..00.... nr of bits = 5
   w ..01.... nr of bits = 6
   w ..10.... nr of bits = 7
   w ..11.... nr of bits = 8
   w 00...... must be 0 for future product compatibility
  r  .......1 parity error
  r  ......1. framing error
  r  .....1.. overrun error
  r  ....1... received break
  r  ...1.... modem status
  r  ..1..... transmission complete
  r  .1...... transmitter buffer register empty
  r  1....... data ready
2 mcr = modem control register
  rw .......1 request to send
  rw ......1. data terminal ready
  rw .....1.. interrupt enable
  rw ...00... normal operation
  rw ...01... transmit break
  rw ...10... echo mode
  rw ...11... loop test mode
  rw ..1..... receiver enable
  rw .1...... modem interrupt enable
  rw 0....... must be 0 for normal operation
3 brsr/msr = bit rate select register/modem status register
   w ......00 prescale = /1
   w ......01 prescale = /3
   w ......10 prescale = /4
   w ......11 prescale = /5
   w .11111.. divisor = /1    = 38k4  with 1.8432 MHz and prescale /3
   w .00000.. divisor = /2    = 19k2    or 2.4576 MHz and prescale /4
   w .00001.. divisor = /4    = 9600
   w .00010.. divisor = /16*3 = 7200
   w .00011.. divisor = /8    = 4800
   w .00100.. divisor = /32*3 = 3600
   w .00101.. divisor = /16   = 2400
   w .00110.. divisor = /58*3 = 1986.2 = 2000-0.69%
   w .00111.. divisor = /22   = 1800
   w .01000.. divisor = /32   = 1200
   w .01001.. divisor = /64   =  600
   w .01010.. divisor = /128  =  300
   w .01011.. divisor = /192  =  200
   w .01100.. divisor = /256  =  150
   w .01101.. divisor = /288  =  133.33 = 134.5-0.87%
   w .01110.. divisor = /352  =  109.71 = 110  -0.26%
   w .01111.. divisor = /512  =   75
   w .10000.. divisor = /768  =   50
   w 1....... brg/ix output
  r  .......1 clear to send
  r  ......1. data set ready
  r  ....00.. always 0
  r  nnnn.... undefined

*end