HD64570 Datasheet, PDF (141/469 Pages) Hitachi Semiconductor – Serial Communications Adaptor

5.2.7 MSCI Time Constant Register (TMC)
The time constant register (TMC) specifies the value (1–256) to be loaded to the reload timer in
the internal baud rate generator (BRG). For details, see section 5.6, MSCI Baud Rate Generator.
This register is reset under either of the following conditions:
• Hardware reset
• Channel reset command
7
6
5
4
3
2
1
0
Async
TMC7 TMC6 TMC5 TMC4 TMC3 TMC2 TMC1 TMC0
Byte sync
Bit sync HDLC
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial value
0
0
0
0
0
0
0
1
Value loaded into the reload timer (1–256)
Bits 7–0 (TMC7–TMC0: Time Constant): The functions of these bits are described below.
• Asynchronous/Byte synchronous/Bit synchronous mode
Bits 7–0 specify the value (1–256) to be loaded into the reload timer in the internal baud rate
generator. (Zero is assumed to be 256.) These bits are used in conjunction with the TXBR3–
TXBR0 bits of the TX clock source register (TXS) and the RXBR3–RXBR0 bits of the RX
clock source register (RXS) to determine the BRG output frequency for transmission and
reception.
The BRG output frequency can be calculated by the following expression:
f_BRG =
f_CLK
TMC
÷ 2^BR
f_BRG:
f_CLK:
TMC:
BR:
Transmit (receive) BRG output frequency
System clock frequency
Value (1–256) set in TMC
Value (0–9) set in the TXBR3–TXBR0 bits of TXS, or the RXBR3–RXBR0 bits
of RXS
Rev. 0, 07/98, page 125 of 453