DS89C420-QCL Datasheet, PDF (133/139 Pages) Maxim Integrated Products – Ultra-High-Speed Flash Microcontroller User’s Guide

Ultra-High-Speed Flash
Microcontroller User’s Guide
AUTOBAUD-RATE DETECTION
The ROM loader can automatically detect, within certain limits, the external baud rate and configure itself to that speed. The loader
controls serial port 0 in mode 1 (asynchronous, 1 start bit, 8 data bits, no parity, 1 stop bit, full duplex), using timer 1 in 8-bit autore-
load mode with the serial port 0 doubler bit (PCON.7) set. For these settings, an equation to calculate possible baud rates is provid-
ed as a function of crystal frequency and timer reload value. Table 15-1 shows baud rates generated using the equation:
Crystal Frequency
ROM Loader_Baud rate =
192 x (256-Timer Reload)
** Timer reload values attempted by the loader: FF, FE, FD, FC, FB, FA, F8, F6, F5, F4, F3, F0, EC, EA, E8, E6, E0, DD, D8, D4, D0,
CC, C0, BA, B0, A8, A0, 98, 80, 60, 40
When communicating with a PC COM port having a standard 8250/16450 UART, attempt to match the loader baud rate and PC COM
port baud rate within 3% in order to maintain a reliable communication channel. If baud rates cannot be matched exactly, it is suggest-
ed configuring the loader to the faster baud rate to avoid the possibility of overflowing the microcontroller serial input buffer.
COMMAND LINE INTERFACE
The ROM loader uses an easy-to-use command line interface that responds to alphabetic commands that are summarized in
Table 15-3. A detailed description of each command can be found in the following pages.
TO PC
TD
RO_IN
RO_OUT
RD _{TOOUT DS232A TOIN}
DTR
R1_IN
R1_OUT
T1_OUT
T1_IN
ULTRA-HIGH-SPEED
FLASH
MICROCONTROLLER
RXDO
TXDO
EA
V_CC
RST
PSEN
HC/AC125
Figure 15-2. Serial Load Hardware Configuration
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