Maxim Integrated Ultra-High-Speed Flash Microcontroller - Manual (Page 162)

15-4
Ultra-High-Speed Flash
Microcontroller User’s Guide
Serial Program Load Operation
Program loading through a serial port is a convenient method of loading application software into the flash memory or external mem-
ory. Communication is performed over a standard, asynchronous serial communications port using a terminal emulator program with
8-N-1 (8 data bits, no parity, 1 stop bit) protocol settings. A typical application would use a simple RS-232 serial interface to in-system
program the device as part of a final production procedure.
The hardware configuration for the serial program load operation is illustrated in Figure 15-2. A variety of crystals can be used to pro-
duce standard baud rates. The ROM is designed to operate across a 3-wire interface from a standard UART. The receive, transmit,
and ground wires are all that are necessary to establish communication with the device.
The ROM implements an easy-to-use command line interface, which allows an Intel hex file to be loaded and read back from the
device. Intel hex is the standard format output by 8051 cross-assemblers.
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 15-2 shows baud rates generated using the equation:
** 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.
192 x (256-Timer Reload)
Crystal Frequency
ROM Loader_Baud rate =
TO PC
RO IN
TD
HC/AC125
TO OUT
RD
R1 IN
DTR
RO OUT
V CC
TO IN
R1 OUT
DS232A
ULTRA-HIGH-SPEED
FLASH
MICROCONTROLLER
T1
OUT
RXDO
TXDO
RST
EA
PSEN
T1 IN
Figure 15-2. Serial Load Hardware Configuration
Maxim Integrated