PORTIBM PC Portable (uses same BIOS as XT) 03A0-03AF - 1st BSC (Binary Synchronous Communication) adapter
Notes:	Initialization of the BSC adapter is performed in a typical
	  sequence like this: Setup 8255 port A-C configuration by writing
	  98h to 383h, followed by initializing 8255 port C by writing 0Dh
	  to 382h. Reset 8251A internal registers by pulsing 8255 port B4.
	  After this the 8253 has to be programmed to the desired values
	  (counter 0 not used, counters 1 and 2 to mode 0). Now, the 8251A
	  is ready to be loaded with a set of control words that define the
	  communication environment.
	8251A: The control words are split into two formats, mode
	  instruction and command instruction. The mode instruction must
	  be inserted immediately after a reset operation (via 8255 port B4
	  or setting command instruction bit6 to 'internal reset').
	  The required synchronization characters are next loaded into the
	  8251A (usually 32h for BSC). All control words written to the
	  8251A after this will load the command instruction.
	     reset -> mode instruction
		      SYNC character 1
		      SYNC character 2
		      command instruction
		      data ...
		      command instruction
		      data ...
		      command instruction
		      ...
SeeAlso: PORTIBM PC Portable (uses same BIOS as XT) 0380h"BSC"

03A0  R-   on adapter 8255(A5) port A: internal/external sensing (see #P0648)
03A1  -W   on adapter 8255(A5) port B: external modem interface (see #P0649)
03A2  RW   on adapter 8255(A5) port C: internal control (see #P0650)
03A3  ?W   on adapter 8255(A5) mode initialization
03A4  RW   on adapter 8253 (programmable counter) counter 0:
		LSB / MSB square wave generator (unused in sync mode)
03A5  RW   on adapter 8253 counter 1: LSB / MSB inactivity time-outs
		(connected to 8255 bitA7, IRQ4 level)
03A6  RW   on adapter 8253 counter 2: LSB / MSB inactivity time-outs
		(connected to 8255 bitA6, IRQ4 level)
03A7  ?W   on adapter 8253 mode register (see #P0651)
03A8  RW   on adapter 8251: data (see #P0652)
03A9  R-   on adapter 8251: command/mode/USART(Universal Synchronous/Asynchronous Receiver/Transmitter) see also UART status register (see #P0653)


Bitfields for BSC 8255 port A:
Bit(s)	Description	(Table P0648)
 7	=1 timer 1 output active
 6	=1 timer 2 output active
 5	=1 TxRDY active
 4	receive clock active (if pulsing)
 3	=0 clear to send is on from interface
 2	transmit clock active (if pulsing)
 1	=0 data carrier detect is on from interface
 0	=0 ring indicator is on from interface
SeeAlso: #P0649


Bitfields for BSC 8255 port B:
Bit(s)	Description	(Table P0649)
 7	=1 enable IRQ(Interrupt ReQuest) A hardware line connected to the interrupt controller chip which signals that a CPU interrupt should be generated. 4 level interrupt (timer 1 and 2)
 6	=1 gate timer 1
 5	=1 gate timer 2
 4	=1 reset 8251A
 3	=1 not used
 2	=0 turn on test
 1	=0 turn on select standby
 0	=0 turn on data signal rate select
SeeAlso: #P0648,#P0650


Bitfields for BSC 8255 port C:
Bit(s)	Description	(Table P0650)
 7 R-	=0 BSC adapter (=1 may be used to detect SDLC??)
 6 R-	=0 test indicate active
 5 R-	timer 0 output (if pulsing)
 4 R-	receive data (if pulsing)
 3 -W	=0 enable timer 1 and 2 IRQ4 and receive IRQ(Interrupt ReQuest) A hardware line connected to the interrupt controller chip which signals that a CPU interrupt should be generated. 4
 2 -W	=1 electronic wrap
 1 -W	=1 gate external clock
 0 -W	=1 gate internal clock
SeeAlso: #P0648,#P0649


Bitfields for BSC 8253 mode register:
Bit(s)	Description	(Table P0651)
 7-6	SC1-SC0	 00, 01, 10= select counter 0,1,2; 11=illegal
 5-4	RL1-RL0	 00= couner latching operation
		 01= read/load most significant byte (MSB)
		 10= read/load least significant byte (LSB)
		 11= read/load LSB first, then MSB
 3-1	M2-M0	 000= mode 0 (for counter 1 and 2)
		 001= mode 1 (not used for BSC)
		 x10= mode 2 (not used for BSC)
		 x11= mode 3 (not used for BSC)
		 100= mode 4 (not used for BSC)
		 101= mode 5 (not used for BSC)
 0	BCD(Binary Coded Decimal) A method of data storage where two decimal digits are stored in each byte, one in the upper four bits and the other in the lower four bits.  Since only the values 0 through 9 are used in each half of a byte, BCD values can be read as decimal numbers on a hexadecimal display of memory or a file.	   0= binary counter 16bits
		   1= BCD(Binary Coded Decimal) A method of data storage where two decimal digits are stored in each byte, one in the upper four bits and the other in the lower four bits.  Since only the values 0 through 9 are used in each half of a byte, BCD values can be read as decimal numbers on a hexadecimal display of memory or a file. counter 4 decades


Bitfields for BSC 8251 data:
Bit(s)	Description	(Table P0652)
---mode instruction (W)---
 7	=0 Double SYNC Character
 6	=1 SYNDET is an Input
 5	=1 Even Parity
 4	=1 Parity Enable
 3-2	Character Length 00=5bits, 01=6bits, 10=7bits, 11=8bits
 1-0	not used (always 0)
---SYNC character 1/2 (W)---
 string of two characters to be sync'ed at (in hunt mode).
---command instruction (W)---
 7	Enter Hunt Mode
 6	Internal Reset
 5	Request to Send
 4	Error Reset
 3	Send Break Character
 2	Receive Enable
 1	Data Terminal Ready
 0	Transmit Enable
---data (RW)---
	any data
SeeAlso: #P0651,#P0653


Bitfields for BSC 8251 command/mode/USART(Universal Synchronous/Asynchronous Receiver/Transmitter) see also UART status:
Bit(s)	Description	(Table P0653)
 7	Data Set Ready (indicated that DSR is at 0 level)
 6	SYNDET
 5	Framing Error (not used for synchronous communications)
 4	Overrun Error (OE flag on when Overrun Error occurs)
 3	Parity Error (PE flag on when a parity error occurs)
 2	TxEmpty
 1	RxRDY (causing IRQ(Interrupt ReQuest) A hardware line connected to the interrupt controller chip which signals that a CPU interrupt should be generated. 3 level)
 0	TxRDY (has not the same meaning as 8251A TxRDY output pin).
	  THIS one is NOT conditioned by CTS and TxEnable (causing IRQ(Interrupt ReQuest) A hardware line connected to the interrupt controller chip which signals that a CPU interrupt should be generated. 4 level)
SeeAlso: #P0652