In-circuit programming of the
Philips 87C576 microcontroller
Author: Bill Houghton
1995 May 03 1
Introduction
The 87C576 includes two separate methods of programming the
EPROM array, the traditional modified Quick-Pulse method, and a
new On-Board Programming technique (OBP).
Quick Pulse programming is a method using a number of device
pins in parallel (see Figure 1) and is the traditional way in which
87C51 family members have been programmed. The Quick-Pulse
method supports the following programming functions:
– program USER EPROM
– verify USER EPROM
– program KEY EPROM
– program security bits
– verify security bits
– read signature bytes
The Quick-Pulse method is quite easily suited to standard
programming equipment as evidenced by the numerous vendors of
87C51 compatible programmers on the market today. One
disadvantage is that this method is not well suited to programming in
the embedded application because of the large number of signal
lines that must be isolated from the application. In addition, parallel
signals from a programmer would need to be cabled to the
application’s circuit board, or the application circuit board would
need to have logic built-in to perform the programming functions.
These requirements have generally made in-circuit programming
using the modified Quick Pulse method impractical in almost all
87C51 family applications.
On-Board Programming (OBP)
The Philips On-Board Programming (OBP) facility has made
in-circuit programming in an embedded application possible with a
minimum of additional expense in components and circuit board
area. The OBP function uses three pins in addition to VCC and VSS
(see Figure 2). The diode shown is added so that in the absence of
the five pin connector the VPP pin will be pulled up above the VIH
level in normal system operation allowing the 87C576 to execute
from internal code memory.
The On-Board Programming facility consists of a series of internal
hardware resources coupled with internal firmware to facilitate
remote programming of the 87C576 through the serial port. This
firmware is provided by Philips and embedded within each 87C576
device. The On-Board Programming facility supports the following
programming functions:
– program USER EPROM
– display USER EPROM
– program security bits
– verify security bits
– specify timing parameters
The OBP function is invoked by having the EA/VPP pin at the VPP
voltage level at the time that the part exits reset. The OBP function
uses five pins (TxD, RxD, VSS, VCC, and VPP). Only a small
connector needs to be available to interface your application to an
external circuit in order to use this feature. The VPP supply should
be adequately decoupled and VPP not allowed to exceed datasheet limits.